Newton,
I use a Duetto DJ100 filter for my vivarium waterfall. It does the job well for the small waterfall I have but there are drawbacks. As the media becomes clogged with debris, the flow is significantly reduced. This is tough since the flow isn't that great to begin with.
In fact, for a large waterfall, multiple waterfalls, or even a large elevation change from pump outlet to the waterfall, I would suggest a dedicated pump.
This way you get something that will most likely have more power for the same price and wont be subject to the same clogging issues as the filter is.
The Duetto DJ100 runs for about $25 USD (around here) with 90 gph max. On the other hand, you can get a submersible like the Rio 600 for the same cost which will pump 200 gph.
On another note, I have had much better luck with Duetto than Fluval anyhow in terms of heat production and durability.
Hopefully that helps a bit.