Separate controllers for each hand is better than a single controller for both
When playing with standard console controllers, I feel my shoulders rounding inwards and my back slouching forwards a bit. The posture that most people assume when holding a controller is not as ergonomic as it could be. I get a back ache sometimes after long sessions of gaming, and always feel a need to stretch my shoulders backwards to relieve the tension.
Having more distance between my both my hands while gaming is not only more comfortable, but improves your posture and let's you game for long hours without aching as much. Which is why I think separate controllers for each hand is better than single controller for both.
I wonder why it hasn't become mainstream when we have so many devices that come as a pair already like earphones.