I think modelers do much better at very low volumes. They don't depend on pushed tubes, speakers moving air, or speakers breaking up, for their tones, so they sound better at very low volumes than a tube amp.
But if you want a really small amp for very low volume playing, there are plenty of choices. I like to joke that my Roland Micro Cube has more gigs on it than every other amp I've ever owned put together. Reason being, I had a weekly gig for around 3 years, that was with an un-mic'd acoustic guitar and vocalist, and sometimes banjo/mandolin and sometimes bass. That gig was as low as 5 people, as many as 30, but usually 10-15. With an un-mic'd singer and acoustic guitar it was plenty loud enough.
That said, I also have a Fender Micro Mustang and it sounds better. It took some tweaking with the computer editor because the effects are overdone big time, but it sounds pretty good now at volumes from quiet talking through loud TV. Very small and light. I carry it in a backpack.
The Micro-Cube wins on batteries. I've never tried the fender because it only lasts 4-6 hours on big batteries (C or D) and the Micro Cube lasts over 20 hours on 6 rechargable AA's. Hard to beat that. When I couldn't plug in, we were playing an hour or a little over every week and I was charging once a month. And the Micro Cube sounds pretty decent. It definitely gets boomy when turned up, but that was easily cured with an old sock in the front port.
But after my last run through with the computer editor setting the effects and gain levels and all, the Fender sounds better and has many more tones.