are you referring to the Mattco tool that has a rotary cutter attached to a long metal strip and you line it up with your matt grid and then you slide the blade along the metal edge?
if yes, then i have one and i like it very much. it eliminates getting that 'v' shape in long strips. also i can cut across my 36" matt, doubled or tripled. saves a lot of time and work. since i cut borders lengthwise i can get up to 108" cuts in one length, no seams. it was about $50.00 +/- and considering how much i've wasted on stuff that hasn't worked well, i call this a good investment.