My original installer review was posted here (follow this link), and the installer was Dore Woodman. That should give you a head start in understanding what they're like.

As for what they delivered, we have a 3 bedroom bungalow with a fairly large extension at the back that is our sitting room, and that probably accounts for about a third of the ground floor area. The extension was added well before we bought the place and was fitted with underfloor heating at the time; a system Dore Woodman were able to make use of pretty much as is. All the rest of the property is heated by radiators; the originals since they didn't need to be replaced.

We had already gone through a process of sorting out insulation issues (new front door, new French doors and so on) and had bought a thermal camera to identify the work necessary. As a result, Dore Woodman were able to rely fairly confidently on what they saw not having any hidden surprises. Their initial visit was reasonably thorough to give an estimate and their second (this time chargeable) visit in preparing a quote was rather more thorough. It was as a result of that that they were able to identify small details that would make a significant difference (such as replacing quite a bit of heating pipework with larger bore piping), meaning the system once in performed as they said it would.

I've just taken a look at the energy used/delivered since installation back in November last year and have seen an overall COP figure of 3.438 which I'm pleased with. All the things other posters on this forum have been bemoaning as "this is best practice; why wasn't it set up like this?" were all done right despite my wife and me not even realising half of them needed to be looked out for, so between the lack of nightmares and the delivering what was promised I'm over the moon with the whole experience.

As for the Ecodan specifically, we were provided with a 5.5 kW model. Although our preference is for a fairly cool house - 15degC overnight up to 19degC for the evening - the ASHP has been perfectly capable of keeping up even on the really cold frosty nights. We do have a log burning stove as a backup (who doesn't like a real fire?) and it's been useful on a couple of days when there were power cuts in helping bring the house back up to temperature quicker than the ASHP would have done; our experience is that the ASHP is great at maintaining a temperature, but unsurprisingly big swings in temperature are not its forte. Nonetheless, other than those exceptions, there has never actually been any need for us to light a fire to help the ASHP keep us warm. The Ecodan has also been set to heat our water to 53degC, and for water heating only to kick in once the tank falls below 45degC. That's how it was set to start and we've never felt the need to change since we've always had plentiful hot water at a temperature that's more than adequate for our needs. I should also add that throughout all this we were concerned to avoid difficulties with our neighbours, and that they have been particularly impressed with how little the ASHP was making itself heard even when going full chat.

All the experience I've gained since installation has led me now to believe that most of the ASHP units are similarly capable and reliable and that the real difference in both performance and reliability hinges on the professionalism and experience of the installer. I'd be more than happy to recommend the Ecodan, but I would certainly not suggest any of the competitors are better or worse options.

Does that help?

@majordennisbloodnok I looked in the Bromley planning permissions website. There are a handful of cases that mention air source heat pumps, but they were suspiciously few, and the one that was reasonably relevant (domestic premises, retrofit) was for a certificate of lawful development as opposed to PP.

By way of background, our application for a certificate of lawful development was denied in respect of the green roof over our kitchen extension due to a stubborn council official unwilling to read the (ambiguous) legislation in light of government guidance. In brief the legislation, read in isolation, creates the impression that converting an existing roof to a green roof is PD but making a new roof green is not - completely absurd. I was too busy at the time with an utterly pointless and drawn out party wall dispute and did not have the mental energy to appeal the decision on the refusal of the lawful certificate. So I have very low confidence in the planning process.

We don't have to use the aroTherm, but our situation is a retrofit of a house which we are in the process of insulating but won't be able to 'test' the insulation / heat demand / size of the existing radiators (which are new but were purchased assuming a gas boiler) for several months. This leaves us a bit nervous about opting for a low temperature system. We need to decide on the system soon-ish to get the works booked and the plumbing/wiring in place before the walls and floors are finished. 

I can easily see how circumstances like those would colour your judgement of how the planning process is applied irrespective of the theoretical intention. Red tape is exhausting at the best of times.

Our house was also a retrofit, so I'm well aware of those particular challenges. I'm not certain, but Bromley might be just about within the area serviced by the installers who did our job. It might at least be a punt to give them a call and talk over; they may well have some good ideas that can reduce the uncertainty and I'd vouch for the honesty of their opinions. If you want their details, just ping me a PM and I can let you know (or search this site for recommendations and you'll find their name anyway).

By way of background, our application for a certificate of lawful development was denied in respect of the green roof over our kitchen extension due to a stubborn council official unwilling to read the (ambiguous) legislation in light of government guidance. In brief the legislation, read in isolation, creates the impression that converting an existing roof to a green roof is PD but making a new roof green is not - completely absurd. I was too busy at the time with an utterly pointless and drawn out party wall dispute and did not have the mental energy to appeal the decision on the refusal of the lawful certificate. So I have very low confidence in the planning process.

We don't have to use the aroTherm, but our situation is a retrofit of a house which we are in the process of insulating but won't be able to 'test' the insulation / heat demand / size of the existing radiators (which are new but were purchased assuming a gas boiler) for several months. This leaves us a bit nervous about opting for a low temperature system. We need to decide on the system soon-ish to get the works booked and the plumbing/wiring in place before the walls and floors are finished. 

In fairness, whilst the planning process is often cumbersome, it's there for good reason and has to have good grounds for refusal. Just because your installation has to be checked doesn't mean it's automatically a "no". I can understand your concern over an obstructive neighbour, but don't forget it's their view that's asked for, not their consent. If their objection doesn't have merit, it can be ignored. I also understand your concern over the planning office itself, but whether that concern is valid or not sadly doesn't change the fact it's a required process.

It might sound a silly question, but do you have to go with Vaillant? As far as I can see, the Mitsubishi 11.2 kW unit is under 0.6 m3 and so wouldn't need planning permission. If there's a Mitsubishi answer, I'm sure there'll be other manufacturers too that come in under the planning permission wire as well.