The Stots template type, which Rutlands sell ("Dovetail Template Master"), can probably be used either way up. I mean either clamped on the edge of the bench or inverted on a router table. It has the additional advantage that you can make more templates with it, to vary the spaacing and make longer runs of dovetails if you wish. It is also very simple to understand and to use. Making it work requires very specific cutters and bearings, but otherwise I think it is a very elegant solution to making DTs with a router.
That said, a Very Nice Man has given me some beautiful dovetail marking guides for Christmas, so mine will probably be made by hand quite a lot inthe near future
PS: Rutlands used to sell a knock off copy. I didn't realise until I looked that they now seem to sell the original instead. It is expensive for what it is (IMHO) but the price does include cutters, although I have no idea about their quality.