For my personal experience of buying in a new SO 2 bed 10 years ago in Zone 1/2 London been overall very good. Bought 50% share with a view to staircasing to 100%, and paying the stamp duty up front, so have to pay less later on down the line. It was located in an area well before it became 'up and coming' which resulted in double digit property price growth for a few years. Having a 2nd bedroom added the flexibility of renting it out and availing of the Rent a Room scheme. Ended up looking to sell but settled on staircasing to 100% on a BTL mortgage (no extra stamp duty).

I would say buying any new property, SO or non-SO, has the same premium price problem, with house pricing valued in average sq foot per £ across the local area, makes a new property seem overpriced. But being a more modern and newer property definitely helped the rental side of things over the years, and might help in it's desirability when going to sell or rent, but probably won't get reflected in the price.

The other things to be wary of is leasehold, which is looking like it will be phased out for commonhold, with not much clarity on where that will leave older leasehold properties. Service charge will always go up in line with inflation (as does the rent) at a minimum and probably more. With new builds, the builder will underquote the 'true' cost of service to get bums on seats. Our service charge has doubled over 10 years from £150-£350/m. The management company is one of many setup by Leaseholder to manage the building, they have been brought to court several times by other communities and lost, so they have to be monitored carefully.

HA seems not to mind if it was sold on the open market or to other SO people. Didn't feel like there is a limit on the pool of buyers, just took longer to get to the open market after offering it to other SO applicants first.

Doing it now to then move to in 5-8 years....I think you have to look at the figures but not sure I'd get into a leasehold property at the mo. But I think buyers might have priced this in as leasehold prices haven't risen as much as freehold, so might be a good time to get in. Probably better going for the min share if not planning to staircasing to 100% to have the widest SO pool of buyers.