What are the advantages of the Cri-Cri's tail and fuselage design?
The T-tail positions the horizontal stabilizer out of the turbulent "prop wash".  This reduces the strength and weight that would be required of the structure if it had to endure the aerodynamic stress behind the two propellers (which is terrific).

This simple shape has everything to do with parts and assembly simplicity and low cost for the homebuilder.  Drag increases exponentially with speed; so for slow aircraft, draggy shaped components are much less a problem.