Right now I'm running the Nomad Factory Free Tremolo (and the full bundle) on a Mac Book Pro that has a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. I run it in Pro Tools LE 8 that runs with a Digi 002R interface. To date I can't say that I've had any issues at all related to performance when it comes to this plug-in. It isn't going to take up much processing power no matter what you're running it on, as it does come in RTAS, VST, and AU formats. Having said this, how well a plug-in will run in general really depends on your system, although I don't think there will be many issues out there.
I'll never complain about a free plug-in, and I don't have a reason to start now with the Nomad Factory Free Tremolo. It actually has a very good sound for a free plug-in, and I think that there's a good amount that you can do with it. It might not be my first choice for a tremolo plug-in, but if I had nothing else at my disposal it would certainly get the job done. If you don't already have the Nomad Factory Free Bundle I'd highly recommend getting it no matter what DAW you've got!