Although the Pure Amps do have the extra features that the GSS, Demeter, and others do not have. There is no DI out on any of the other small standalone mono amps, as far as I know, as well as no 9V outlets. I think all of them have a single gain control. The separate gain and volume would allow you to plug most, if not all, basses directly into the input with no separate preamp needed.
If the Pure Amp 350 were available, I would pick one up, since I have a pretty decent collection of tone-shaping and other pedals that could be used in front of it.