@editor Have gone with Octopus Energy in the end. Comparing the two quotes, I don't see anything significantly different in terms of what will be installed. So, I assume the extra Aira cost is for the 15 year comfort guarantee. Octopus obviously have the economies of scale, and average the costs over the many thousands they install.
Mrs had to be convinced about the looks though! The Daikin heat pump doesn't look much different from a heat pump we used to heat the above ground pool with, until it was turned off for good. Agreed Aira looks good, but not worth paying almost double what Octopus quoted us.

Sorry, forgot to add the thought process. 
The primary factor being how long the heat pump manufacturer has been in the sector, installation costs and reputation of the installer. Would have loved to go with a HeatGeek assured installer, but couldn't justify the cost differential. As ours is a relatively new build and standard installation, couldn't justify the need for the assurity in terms of top notch performance. Would have gone with Aira has the quote been just 1.5 times, but 2X is simply too much to ignore just for the looks.
Also, the fact that Octopus being a big player would have the resources to service and emergency repairs, all adds up. Good reviews from the likes of Speak to the Geek and Jonathan Tracey on YouTube helped with any concerns over quality. In general, I haven't seen any horror stories on the media about heat pump installations by Octopus. So, they are doing something right. It may not be the most efficient, but seems to work.

Posted by: @chandykris

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@editor Have gone with Octopus Energy in the end. Comparing the two quotes, I don't see anything significantly different in terms of what will be installed. So, I assume the extra Aira cost is for the 15 year comfort guarantee. Octopus obviously have the economies of scale, and average the costs over the many thousands they install.
Mrs had to be convinced about the looks though! The Daikin heat pump doesn't look much different from a heat pump we used to heat the above ground pool with, until it was turned off for good. Agreed Aira looks good, but not worth paying almost double what Octopus quoted us.

I noticed a few days ago on the Aira app that there is now an option to drop the thermostat target temperature by up to 3°C during the night (user configured time boundaries). Certainly resulted in a more comfortable nights sleep at Chez npru.

@npru Aira proposed 7 radiator changes, so need to see how many Octopus propose to change. Highly likely at least the radiators in four bedrooms need changing.
Will keep you posted on the progress. It would be good to get it installed this winter season, as our heating is usually turned off towards end of March. I want to test the system over colder temperatures if possible rather than wait until next October.

@npru It is worth bearing in mind that OE offer a very reasonable service contract too. Toodles.

@toodles Yes, read on Octopus website that the annual maintenance plan is about £108. That's less than 1/3 what British Gas charge us for boiler servicing. All these savings stack up!

@chandykris Indeed, and I think that it is likely the service will be somewhat more thorough than any gas boiler service that BG ever carried out for me! (At well over £400 per year at that!) Toodles.

Sorry to circle back to this discussion again. I may need only a couple of radiators (or less) to be changed if Octopus insist on 50 degrees flow temperature. Playing around with HeatPunk, I see that even at 45 degrees flow temperature I may need only two radiator changes. That kind of skews my decision matrix as I would be comparing apples to oranges if Octopus aren't going to change any radiators vs Aira offering as many changes as my system design demands. Aira is also happy to offer two changes as part of their discounted quote which is about 1.5 times Octopus' quote. Aira's original quote was double Octopus' quote.
Could anyone with an Aira heat pump installation please confirm that they haven't taken any annual maintenance or servicing plan, and it's all covered until the 15 year warranty. Appreciate your thoughts on the same. If that's the case, Aira is still slightly more expensive, but then I don't have to pay any annual servicing for 15 years.  That can justify the slightly higher upfront investment costs.

@chandykris we have a AIRA HP and they told me that everything is covered. We can clean the magna filter ourselves and they show you how to do it. Any problem then they will just come out and fix or replace.

@bromide Thanks, that's good to know.

@chandykris we had an Aira HP installed early November and have also been told that everything is covered under the 15 year warranty. 
We had a slight issue with a fault after installation too and they came over numerous times to sort it out and were very helpful