I've used the internal/external eheim pumps if that is what you are talking about.
IMO they don't put out much flow for the price/size though. If I were to go with an exteranl pump I'd rather go with a Velocity, Dolphin or something designed for external only. The inlets and outlets on the eheim are tiny.
I gotta rant here for a sec too. I wish all these manufacturers would get away from using thin plastic to make their "external" pumps. I hate it, go back to making the old metal housings that didn't crack or bust the threads when putting piping on them...
End of rant..
Mike