Rotatrim Mastercut II. If you make the investment your cutting wheel will be sharp and last for decades. Don't judge the concept by an abused institutional model. The Rotatrim comes with a sliding stop which assures that all 4 edges will be square. Just mount the tissue a little eccentric, so it doesn't overhang on one edge. Make your first cut 90 degress to that edge and all the others will be square. I also have a Logan mat cutter but visibility is poor and damage to the print can occur.
I too like to float my prints, and there is no better way to do it than the Rotatrim.

Elmo Schmidlapp
Director of Marketing
The Rotatrim Corporation