I've been in a Group for over 24 years, and it's the answer to low cost flying.
The only minus is selling your share can take time. For anyone who thinks a tight legal agreement is needed - look at the value of the share compared to legal costs. Consider what you write-off annualy in a car's value. I put my 2013 flying costs on another PPRUNE thread.
http://http://www.pprune.org/private...ml#post8546012