We had shared ownership. It worked for us, but I don't think it's ideal. Some of our neighbours on the same scheme didn't have the same experience as their circumstances were different and it ultimately caused issues.
I think it works in certain circumstances but not all. We have our doubts about whether it works in a market where housing prices are declining for various reasons. If you end up in negative equity you can get stuck much more than if you own the property outright - precisely because you can't rent it out. It limits your alternative options. I would strongly encourage having a decent deposit to at least insulate against this - and enable you to sell for a small loss if you absolutely needed to.
Be aware of any additional fees due (service charge, leasehold charge, rent) and more crucially if they do, how the increase is calculated. There have been numerous cases where horror stories have been well publicised.
My biggest piece of advice: Every scheme is different; it's a minefield. For this reason get a solicitor with experience with shared ownership. Don't just go for the cheapest option.
It's worth the investment. Understand property the terms and conditions for what you are buying - if you don't you could leave yourself potentially exposed financially further down the line. Equally be open minded going into it, and be prepared to walk if there's some sort of dubious clause / doubt in your mind.
I personally think they work better for people planning to stay somewhere for a good number of years rather than just a couple of years (we had ours for over 12 years). This means thinking about whether / when you want children/ more children. And looking at how likely a relocation might be (related to job security) OR for people where renting is the only other likely option and want housing security.
I don't think it's such a good bet for people who think they are likely to get another house in the next 5 years if I'm honest.
I think that shared ownership has it's place. It's flawed though and some people end up in a difficult position. I've heard of a few people caught out for various reasons.
And yes it's a fixed price sale - no haggling. This creates its own issues too if you come to sell on. Housing Associations are extremely reluctant to reduce an asking price once a house has been valued. So if you do want to sell on, you don't necessarily want the highest valuation possible because that might mean you end up over pricing yourself out of the market. Trying to persuade a HA to do a revaluation once an initial sale price has been agreed by you and them isn't easy. I've heard of one friend of a friend who were stuck for 4 years because of this, before the HA eventually agreed to drop the price.
Dealing with HAs isn't necessarily easy generally. I have to say ours ranks as one of the worst institutions I've ever had to deal with. Truly beyond useless. I was very glad of the day I knew we'd never have to deal with them again.
Shared ownership was ultimately the right thing for us as I say, but I do strongly caveat that too.