I opted for the center stick in the 650 because with the wide console, leg room is quite restricted.  Dual sticks take up a lot of that room; especially with 2 on board.

I have the dual stick option in my 750 STOL and I now wish that I had built it with the Y stick. The Y stick is easier to build and more importantly, more comfortable to fly with (IMO).

In case you decide to install the dual stick, I have a brand new never used kit available. Powder coated( red) sticks and urethane red control rods, plus assembled brackets. 

Barry