They are good for use as a little keyboard submixer on live gigs, but that's about it. And chances are they will break with road wear. The faders get noisy very easily. The inputs are all mono, and there is no panning, so it is not useful for stereo applications. Of course, I could be thinking of a different model: the one I'm thinking of is about the size of a deck of cards, black, with four mini-faders.
One Rolls piece that's not bad is the little 4-channel headphone mixer. I've got three in my studio, in addition to a couple of Fostex's. I think the Rolls sounds better than the Fostex.
If I needed a little submixer for stereo sources (in non-critical applications) I'd probably just grab one of those tiny Behringer, Mackie, or Soundcraft sub-$100 mini-mixers.