If its this:
http://www3.towerhobbies.com/cgi-bin...?&I=LXHZ30

the picture shown is the top... of the device

how you use it:
for example trimming the leading edge of the wing or anywhere you want to make a straight line with your covering ( sides of plane body,etc )

tack your piece of monokote or whatever in place on all sides, you can either tack or mostly seal down the edge that you're getting ready to trim

place the tool with the blade against the covering and the base of the tool against the body of the plane....
run the tool along the seam being trimmed... it automatically produces a straight cut line, with about 1/8" overlap that you can then iron down.


I think the main draw back with it is it's use of #11 exacto blades which I never found great for cutting coverring, much prefer razor blades