Bitter - which flashes were you looking at? The ideal is the older MT24 EX flash - however that runs at a pretty high price; good and very convenient, but costly. There are are cheaper setups you can use, but they will require more DIY setups to get them to function well with the MPE.
As for the two - I've always seen people that get fisheye lenses rave about them for a month - then forget about them. They seem to be a more short lived thing- that said the MPE is very much a love or hate lens - you'll either love it or you'll hate it.