I have the Butterslax and matching 212/215 cab. Its not my favorite amp, but it is my favorite amp for some things.
Compared to my Buxom betty, obviously there is no comparison, Betty is clean and Butter ain't... That said, I have a Diezel VH4 pedal, a BE pedal, an SLO pedal and a host of others. Betty with a dirt box sounds great, still doesn't sound like the Slax... And while Slax can't get clean like Betty, it can get clean enough, with single coils, to do what I want.
Compared to my JJ100, again JJ has more "Clean" but its clean isn't exactly clean either. Comparing gain channels, the slax is tighter, with a much faster attack than the JJ. Its nice to have a true third channel. My JJ is modded for footswitchable JBE mode and volume. Its close to a three channel amp, but I dont have the gain control mod so channel 2 is already "high gain" to get JBE mode where I want. Slax lets me have a true "mid gain" on channel 2 with "high gain" on channel 3.
I love what it does in my rig as I blend it in with my other two amps, it adds something neither of my other amps has so it has a functional purpose. If I had my druthers, I wish the sat switch was footswitchable on channel 1 to make it mimic a 4 channel amp and get closer to a "clean" tone on channel 1.