A paper cutter is not a car.
I saw a Saunders at a camera shop today and had regrets having purchased the more expensive Rotatrim a month or so ago (found this thread when looking to compare the two).
The Saunders seems to have the same blade system as the Rotatrim, dual rails, and is made of metal where the Rotatrim baseboard is made of MDF (fibreboard).
The Rotatrim is nice, but doesn't seem nicer than the Saunders.
I'm unhappy with the plastic guard on my Rotatrim. I use mine for cutting sheet film among other things, and there is the possibility of scratching the emulsion when moving the film under the guard. I removed the guard but that rendered the cutter useless. The guard is necessary to hold the item flat, otherwise the item moves all over while cutting and a clean or useful cut is not possible. When removing the guard on the Rotatrim I was unimpressed with precision of the screws, the strange, haphazard, cheap spacers/shims, and the screws screwed right into the MDF (without precision so not exactly straight), there were no screw anchors, it seemed rather shoddy actually for such an expensive item.
I bought it to replace a rather low-end Dahle which kind of sucked, the straight edge was not straight and therefore the Dahle did not cut straight due possibly to needing adjustment (according to Dahle customer support), but the screws to do this adjusting are star screws, and I only have flat and Phillips-head. Plus it is mostly plastic.http://www.bhphotovideo.com/c/product/511185-REG/Saunders_890_018AS_Professional_M3_Rotary_Trimmer.htmlhttp://www.bhphotovideo.com/c/product/251598-REG/Rotatrim_RC_RCM18_Mastercut_II_18_Rotary.html