It is at least a good, cheap option. Another option is getting a FW400 to FW800 cable, for the slight convenience of not fiddling with an adaptor dongle. And since FW cables and sockets are "symmetric" (rather than having an "A" end and a "B" end as with USB printer cables), there is only one type of such cable!
In fact, I use both an adapter and a FW400-FW800 cable. I think the latter option is more convenient, the connection is more secure and it's more compact (than the FW800_to_FW400 adapter + FW 400 cable).