One thing to keep in mind with a volley: Compared with a ground stroke where the racquet sweeps more around the player's body through and arc, the compact move of the racquet in a typical volley (a good one) is more linear as the racquet descends forward through the ball. Lots of the control of that shot depends on that racquet movement, which is more straight through the ball than with a stroke.
With two hands on the racquet, the only way you can move it through the ball is by turning your shoulders, flipping the racquet with your wrists, or by using deliberate footwork to carry you forward. Since you're holding the racquet while moving forward, the racquet moves, too. That's where the energy comes from with pretty much any solid volleying technique, so I'd say that if you try this technique, good footwork is essential to make it work.
Can the two-hander work well? Oh yeah! I've been toasted plenty by a young lady with a remarkable two-handed backhand volley that I sometimes get to play against. Pretty sure that she used to play college tennis at BU, so I should also add that she has especially good footwork and movement to help with this shot. Two hands can be clutch when fighting off a ball with a reaction volley, but I still also agree that this volley style is limited.
With proper forward weight transfer through the backhand volley, I believe that the one-handed technique compounds the racquet's movement through contact while maintaining the proper orientation of the racquet face (slightly laid back). That means a greater potential for zip on those volleys along with more directional control... and touch.
While I understand what our pal Nellie was getting at, I could also argue that a two-handed style would often encourage more active wrists through the shot, since there's more leverage available. That could make for lots of bad volleys, but good guidance and decent technique can make that volley work.