The short - GAT DAMN.
The long -
This thing is one FUSSY LITTLE BITCH when it comes to power. My BBE Supah Charger has 8 individual power receptacles, 6 of which will run at the Tube Cake's native 12 Volt supply. The first slot I plugged it into it went bat****************. Like, noisy, making burble noises if any notes came through it. Really ****************ed up. I plugged it into the second slot off the main and then it was crystal clear. So, if you don't have good, steady power, it would be pretty worthless. I may have to test out the BBE and make sure it's providing correct voltage on all slots after this little trial.
Anyway, once the power issues were sorted, which I won't hold against the Tube Cake as my supply is also new over the last week, I put it through its paces. My plans were to have a nice late night br00tz machine for fiddling with after the wife goes to bed, and possibly have a good recording rig that sounds at least a little tubey without blowing the windows out. For that, this little bastard excels.
I ran an R1 and a P1 into the front (one at a time) both boosted with a Bad Monkey and unboosted just to test out the tones to be had. Up to about a quarter of the way up the dial on the Tube Cake you've got good low volume tones, but what surprised me was from that point on up you start to hear a change in the tone, not just the volume. Everything starts to get a bit more crisp up top and a bit more lively all around. At about halfway up the dial it's into the volume range where I probably wouldn't play it in the middle of the night due to others in the house. All the way up it's shockingly loud for 1.5 Watts Solid State. Will it alert the neighbors? It might, but mostly in the, "oh, someone's playing guitar" way not in the, "god damn mother****************er I'm calling the cops" way.
I doubt it would keep up with anything but the tamest drummer, so unless you're mic'ed up it's not gonna be a good substitute for your live or rehearsal rig.
The most impressive part of it is the way it changes as the volume comes up. It becomes very dynamic and really breathes higher up the dial. There's a very smooth taper to the master volume that gives complete control from all the way down to all the way up. The presence and depth knobs have a real effect on the tone no matter where the master is set. I found the presence very pleasing at the lower master settings and a little harsh at higher volumes. The depth just adds a big low end fatness. With the P1 it became too much above half and started flubbing, with the R1 it sounded good a little higher. This could be the cabinet/speakers I was using at the time.
Basically, you want a monstrous tone at controllable volumes, use one of these with a preamp of your choice into whatever speaker sounds good to you and you should be in business.
I should make the disclaimer that I left the preamp masters at about 1/4 volume throughout this little trial. There's probably more volume to be had in there if you tweak your preamp, but I still wouldn't say it's gonna be a screaming stage rig.
There is also a three watt version of this amp available. I have not had the opportunity to play one of these to note if there are differences or not.
Pretty much, for $140 plus $130 for one of the preamps, you could have a nice little practice amp that just needs a decent speaker to perform well without making your roomates/SOs/dogs/cats/and neighbors hate you. It's certainly a better late night rig than the old 5150 was.