I had that bag when I started commuting. Topeak's system works fine. The trunk bag is insulated, which is a nice feature, and the fold out panniers can hold a bit of stuff. It's definitely not the setup you want if you plan to do any sort of shopping, because the panniers aren't large enough.

It didn't survive when I was hit from behind by a truck. The rack bent and the one of the panniers tore off. Now I use a Tubus rack and Carradice panniers.