I have a shop made guide - aluminum fence glued to 1/4" masonite. I think a key is using a Porter Cable 314 trim saw on it. The saw is sorta underpowered for frequent use but the base is quite a bit longer than it is wide. Circular saws can be the opposite - wider than it is long. The little P-C saw tracks very nicely along the aluminum fence, no tendency to cock or move away from the fence. Having said that, the Griz track saw would be pretty tempting for not-too-heavy use.