I did something very similar to you. Finished my PPL then bought a £10k share in order to facilitate hours building towards a CPL including some Aerobatics and the Night Rating.
The warning I would give is that I have now found myself with a very large amount of my training budget invested in a liabilty that, in the current climate I am likely to find difficult/impossible to sell.
On the other hand it is a very well run and active group and I have gained a huge amount of extra knowledge, experience and had a wider range of flying opportunities than I would have got from simply hiring from your average club.
I would say that if you're going to buy in, don't bank on being able to sell out in less than 5years and not make a loss on your investment that will outweigh any hourly saving. Buy into the group rather than the aircraft as the maths is never likely to add up to buying being cheaper.