It makes no sence to buy shares with the current BTC rate:    

18	$/BTC - current rate
5,000	shares
39	rigs (lets go with this number for now )
128	shares/rig
0.75	BTC/share
1,731	$/rig
50%	%revshare (since 50% goes to the owner)
3,462	effective cost of rig

   
 VS.    
   
 1,200     $/rig - buy my own
   
 2.88     Ratio

Thats overpaying by almost 3 times
   
At the original  7USD/BTC - it was competitive,    
but now you would have to cut the share price to something like 0.25BTC/share to make it work

Please comment?