There is a M&S development in my village. It’s really nice with lovely gardens and many flats have balconies overlooking it or the neighbouring fields.
When flats come up for sale they do seem to sell reasonably quickly, but notebly not at price when they were new 7 years ago (between £300-450k).
The most expensive seem to be selling at the £300k mark for the 2 beds with balcony - a steep drop for anyone who bought new. But they do seem to sell if priced correctly.
The fact is (especially new) they are never going to be a good investment like most conventional properties and many fail to sell because people want what they paid or won’t accept serious losses.
So the key is to be really clear about the pros and cons and there are pros - they are just not financial.
I think the development itself is a big factor. Some are much nicer than others and in better locations that are liable to be easier to shift than others.
I’d be very wary of buying new and also in a development where there are lots for sale already.
As pp’s have also said timing is a big factor. So many leave a move like this too late - almost at the point of needed residential care and that’s a mistake. It’s a massively expensive choice if you expect only to live there for a few years.
On the other hand having the on-site facilities (the one near me has a cafe/dining room/guest apartments/lovely gardens/great transport links in a thriving village with lots of local amenities) when you are in a position to enjoy them for 10 years or more (and can afford the charges) is about the lifestyle it provides rather than the money.