I'm in a SO property, bought last year. I did a hell of a lot of research before going into this. I'm in the south east where house prices are crazy high and so even though I had a deposit to use a help to buy loan, the mortgage was impossible. I would only advise shared ownership on those who are projected to be in a position to buy a whole property within 2-5 years, be it the other part of the house or a different property. The rent increase (mine is 5% this year!)Will quickly become unaffordable if your income is stretch and only keeping up with inflation. Note if you fall behind on rent then the housing association can evict you and sell the property and you are not entitled to your share by default!! I would also look at how quickly resale properties go and what % they're selling at. In my area they sell quickly because so many people cannot afford whole properties, but I would not touch SO in any other part of the country because the demand/need isn't there. Then if you want SO still, make sure it's one where you get the freehold on 100% ownership without any extra cost.
To give more context so you know why I did buy mine. I'm in a very good early career and my DP is an apprentice, both of us will have pay increases so that in 5 years we can buy a full property. We're also in the position that in 2 years we could buy else where in the country rather tha the expensice SE. We went for a big enough place that if our circumstances changed we can still afford our home and it can become our family home rather than a stepping stone.
If it wasn't for the near guaranteed career progression I wouldn't have gone for it. With this year's rent increase some families who have been in SO for 3-5 years are now forced to sell up because they cannot afford the rent.
Make sure you work out, if your salary doesn't change for 5 years, can you afford increases in rent at 5-6% each year? What about when you come to remortgage and the interest on that has gone up too?
Plan for at least 5 years and remember house prices may fall in the coming years because of brexit so are you prepared to make a loss on the property if you are out priced?