From personal experience, albeit limited, you need to be very careful. If you are, it could work out great. If not....
I joined a group 18 months ago. The group had been going over 18 years and had relatively little turnover of members. The aeroplane was superb - allegedly one of the best of it's type in the country for it's age.
I was assured the funds were healthy. I should have checked the details, but felt confident that I was getting into a sound ground with good business acumen.
Some 18 months later the group has been disbanded and the aircraft sold. Thankfully I still have access to rent the same aeroplane, but in the 18 months my share value reduced by over £1k. This was because the aircraft had a great deal more debt (for upgrades and engine repairs prior to me joining) than I was aware of.
In the end a number of members decided to leave, just as the star annual became due. With no money to pay the inevitable bill, the group was faced with no alternative but to sell the aircraft to clear the arrears. Bringing in new members to replace those wishing to leave became impossible because of the debt, and without new members we wouldn't have enough money to clear the debt (and aircraft utilisation would have been insufficient to make it pay for itself). Ye Olde Catch 22...
So I'm back to renting, which at least has the advantage of meaning I know what I've got to pay, and the bill for any repairs, maintenance and upgrades is of no concern to me.
I would consider entering a group again, but I would go in with my eyes open much wider next time....