Don't let all of this put you off. All of my group experiences have been great.
Do understand planes break all of the time and dips are not unusual. Just factor it into the hourly flying cost.
I never understand why so many people have shares but never use them . They pay the monthly £50 and fly once a year. Thats £600 per hour before any dips or variable costs.
Be focused, plan to be in it for a fixed period plan to do a certain number of hours then plan to get out.
Don't join it fly a load of hours in the first month then don't fly it for the rest of the year. Renting is much cheaper.
Of course there are other reasons to join groups. They give you access to stuff that can't be rented like Yaks, Jets, Lots of aerobatic and single seat a/c.
As everyone says , ask the right questions and go in with your eyes open.