I'll throw my hat in the ring (how do you like that WWI reference, DR-1?); I've got three planes with inverted Saitos, and none of them really need it for running. I've got enough time on the engines and they're tuned well enough that they run like well-oiled machines (DUH). That said, I have on-board glow drivers on two of them. I did it because both of them do a lot of air time at low throttle settings (1/3 or less); I have a lot of build time in one and wanted utmost reliability, and I fly the other one over water, and I wanted utmost reliability (do I hear an echo?). I've pretty much resorted to just using them for start-up, as the glow plug is inaccessible because of its position on the inverted head, and fully cowled installations.

If you need easier access to your plug, you can get by with just a remote glow plug attachment. The MPI one mentioned is a great one, it's what I use and I like it. If you do decide on a remote driver and don't want to make your own, MPI makes a really nice one (Super-Glo) for as cheap as $45.