Here's the latest Fogstar ready built pack. £1849 (although has been cheaper and will likely be cheaper at some point when they have their next sale/discount code).

It's the same Seplos V3 BMS you have.

It has a 6 year warranty (and 10 year Fogstar support) and not double the price of those unknown eBay packs that you listed (which didn't even have a breaker, let alone any future support or warranty and an unknown BMS)

It has a heater and fire protection as a new upgrade.

It also includes 50mm cables to daisy chain, or add to a busbar.

You should be able to pick one of these up for around £1500-£1600 in the next few months when they go on sale.

I know which I'd buy.

It is up to each individual or company to decide on what they see as comparable. Having said that, @transparent ´s post above outlines key aspects that matter to domestic and commercial users. 

Having experienced the Fogstar DIY route, I now have a strong view that a ready made battery is the one that suits a simple minded person like me. 

It saves time, if it fails the supplier provides the warranty, not many questions asked, etc. And often they are also cheaper. 

Thus I could order a steel enclosure which is pre-fitted with a JK BMS unit with 2A active balancing, a JK touch-screen to configure it, and a pair of Anderson connectors for the power leads.
I can then ask the same supplier for a set of sixteen 280Ah Grade-A LiFePO₄ cells to be shipped in separate boxes, ready for me to install.

Or I could buy those same 280Ah LiFePO₄ cells direct from EVE themselves.

Either Eve or the first Supplier might already have stock in Poland or Turkey, which can be shipped to the UK faster and possibly with lower import tax. 

It's a free market.
The goods are normally priced in USA dollars, which means the total in pounds sterling fluctuates slightly each day.

I may or may not be able to obtain a price lower than a battery from Fogstar with the same capacity.

But I also ought to consider what I'd do if something went wrong with stuff I'd bought directly from a Chinese Supplier.

In my experience they are extremely polite, and will endeavour to resolve a problem.
But if I need to replace one 'duff' cell after 15-months use, there will still be the need to provide evidence that it isn't my fault.
Plus there's carriage charges and shipping delays to consider too.

I actually have spare new/unused LiFePO₄ cells here.
If there is a fault, then I want to be able to resolve it the same day,
and then worry about contacting the original supplier later!

What I wouldn't like to do is buy a prebuilt battery which only has a (Chinese) brand name on it.

Even if I have Ebay & Paypal customer protection for my order, I'd have no idea if the BMS unit would be compatible with my inverter(s),
nor the quality, and recharge-lifetime of the cells.

For obvious reasons it isn't possible to compare such batteries with others.
We'd have no idea if the comparison is 'fair' or like-for-like.

Thank you.

Competition is what keeps big companies like Fogstar on their toes.

Whenever anyone suggests, implies or states that Fogstar are not twice the cost of alternative options despite all the evidence, this is misleading to others.

No-one did.

You posted some links to items that may or may not be relevant and comparable, tried to get someone else to find updated links when it was pointed out the ones you posted were obsolete and then tried to suggest others weren't being helpful.

To date, you have not yet demonstrated the other batteries you found are reasonable alternatives to the Fogstar. They might be, but they are currently complete unknowns; there's no track record to point to, no-one has any experience of them, there's no documentation to see and there isn't even any guarantee they meet British safety standards, let alone confirmation they do what they say they'll do. All these are reasonable points for discussion but until they are addressed the batteries are not half-price alternatives to Fogstar or any other known brand; they're pictures on a web site with a price attached. What IS misleading to others is to put them forward as viable alternatives before their comparability is demonstrated.

Competition is what keeps big companies like Fogstar on their toes.

Whenever anyone suggests, implies or states that Fogstar are not twice the cost of alternative options despite all the evidence, this is misleading to others. 

One of the key benefits of this forum - I'd even go so far as to say a defining feature - is that people are allowed to have differences of opinion. @batpred, you need to be aware that @bash and @swwils are not alone in having had good experiences with Fogstar, and telling the forum of good service does not equate to membership of a "fan club". You are in the minority in your take on the company and its products, but, in line with the ethos of this forum, you are entitled to your viewpoint. You are not, however, entitled to use snide jibes at the expense of others who feel differently. Nor would I accept jibes in the other direction at your expense, but so far I haven't seen any.

To all, please let this thread return to the informative discussion it was.

In all fairness you haven't provided any help at all, just links to some unknown and untested batteries from a random eBay account.

Of course it is not helpful to frogstar fan club members to show that there are plenty of ready made batteries models that are sold in the UK for half the price! 

In all fairness you haven't provided any help at all, just links to some unknown and untested batteries from a random eBay account.

It would have been more useful to have given first hand information on these cheap batteries, but unfortunately although you seem to think they are the way forward, you haven't bought any yourself.

Please do though report back on your findings when you have bought some.

Please post new links, it will help others.

Erm... how can @jancold post new links?

It's you @batpred , who is doing the research into cheaper storage batteries from online sellers.

ermm.. I do not have a monopoly on helping others to save money...   

Please post new links, it will help others.

Erm... how can @jancold post new links?

It's you @batpred , who is doing the research into cheaper storage batteries from online sellers.

Isn't it the case that you're comparing Chinese-based manufacturers such as Datou Boss?

But how are you assessing the compatibility of their integral BMS with your existing Fogstar/Seplos battery and your Seplos inverter?