I bought my SO house in 2018. 3 bed semi. We're in an area where house prices vs salary are the worst in the UK. We had the deposit to buy a 3 bed new build using help to buy scheme, but not the salaries to get a mortgage. We were 2 years off buying a whole house but obviously couldn't forecast that, and to be honest I no longer like the idea of a HTB loan. We are hoping to buy the other 50% this year provided the house value hasn't dropped and our LTV is within the criteria of our lender.
The advice I give any one buying SO is: do you have the means to buy it outright or move to a property that you can own outright? By this I mean, are you early in career and you have a greater earning potential, or can you afford a mortgage you can pay down quickly, to get enough equity in your share to get a mortgage for the 100% or other property?
If you do say yes to the above, shared ownership could be a good step. You want to make sure you get a freehold at 100% ownership of the property (not applicable to flat) and that you are not capped on your share (some cap ownership at 80% etc) this is because you want the house to be yours if you buy 100% and also at sale to be able to sell on the open market. There are lots of T&Cs to read up on in the contract.
Note, also, if you go to sell an SO, and you sell for less than the value given at valuation by the housing association survey, your share has to cover the loss to the HA. E.g. if you own 50% and you want to sell. House is values at 200k. You accept and offer of 190k. 50% of the valuation in 100k, from your sale you owe HA 100k. You would only take away 90k from the sale. In extreme cases this could significantly reduce your equity and even put you in negative equity. Effectively unable to sell.
This brings me onto my next bit of advice. Only buy SO in areas with high demand - it makes resale easy and SO properties aren't normally negotiable to SO buyers, so the above is unlikely. In less popular areas you can sit on the market for a long time.
Third bit of advice, choose a good housing association to buy with. This can make or break you SO experience. We have a good HA, they are their for their residents. Not perfect, but they listened, our rent increase YoY was reduced retrospectively because we complained and they listened. The other HA in the area is awful for SO and so are some of the big national SO ones.
Also consider:
Are you a ftb and close to 100% within 1-2 years on a house with no compromise on size etc?
If you say yes to the last question, you would probably end up spending as much on fees and stamp duty buying and selling in a short time, as you would on rent to save for 1-2 more years.
And remember if you do SO, rent increases YoY. If you are struggling with the costs when you buy, you can be priced out. Some people have had to sell and go back to rented because they couldn't afford the rent increase on the SO after 5 years of increases. When we bought, we made sure our salaries at the time would not be stretched after 5 years of rent increase and that we could extend our mortgage term to lower monthly payments if needed.
I hope that helps. For us it's been great and we are glad we did it.