For 1/4" overlaps between 2 large color breaks I use a straight edge an a blade. For trimming a nice 1/8" overlap for a fuse or control surface the Higley Trimmer can't be beat. I've tried all of them, the Monokote trimmer and DuBro even had one they marketed a while back. The Higley trimmer just works. It's simple, blades are cheap and it's versatile. I think I paid abut $10.00 for mine. IIRC he was at a local swap meet when I bought it. He has some other gizmos that are pretty simple and useful like his wire benders for small diameter music wire.

If anyone is interested in covering videos that aren't hour long infomercials check out Charlie Bauers covering videos. He was the product manager for Top Flight back in the early days and he did a set of covering videos are better than anything I have seen to date. Although they are a little dated by today's standards (Charlie looks like a different guy, much younger) the information is still good. I learned with the first 2 in the series back in the early 80's and still use a lot of the techniques in the vids.