I've been edge trimming with my routers for years & never needed such a device. I worked in a big shop in the early 90's & first saw this method I use. We produced alot of commercial millwork, & the countertops often had wooden edges, no matter what the surface.
When I got there they had an old & large rockwell router (pre portercable, think about the 3 1/4 hp fixed base PC router in silver, with no plastic). It was in it's original fixed base which was fastened to a double sub base plate. The upper most base plate was a full base plate which extended away from one side of the router about 12". To the underside of this base plate was a second 1/2" thick plate that only extended away from the bit & doubled up theextension of the top plate. Now to look at the underside of the router base, you'll see thescond base is triangle shaped under the router itself, & partially surrrounds the cutter. This leaves the cutter, protruding through the top most base plate, exposed about 240 degrees or so.
A handle is added to the top of this sub base next to the fixed base, but out on the extension. This base is total maybe 3/4" thick.
To use it you must first adjust a 1"diam. end mill type cutter (or a large diam. plunge bit) in your router to just kiss a piece of paper set under the router (not the base plate). Next place the router on your counter top & proceed to trim down the exposed edges, a papers thickness away from the surface.
This works very well in that the cutter action in relation to the grain of the edge is optimal. If you cut from the side with a rotating cutter you'll tear up the grain. That sucks

. With the router on top but cutting with the underside of the cutter, you'll get perfect results. Plastic laminate on the bottom of the sub base is a good way to always move smoothly about with the router.
I only use a card scraper to clean off the machine marks, a good end mill cutter in your router will leave few, & there is no grain tear out ever. I saw a great cutter for this in the eagle catalog I just got recently. They even described it as such.