You'll see from my signature that I still have a Walkabout and a pair of M-Pulse 600's.
I am probably not able to give a great comparison. That's because the Walkabout hasn't ever been used as a standalone amp, always in the combo. The physics of that (the down-firing radiator etc) mean I would be loathe to give a definitive view.
Having said that, I love the sound of that combo so I'm perfectly happy with that. I went from a B400 to a 400+ (for the sake of clarity, I had both the 400 and 400+ - the latter had gone when this was taken) and then the M-Pulse. Aside from the fact I found the 400+ a little more detailed that the 400 I have found that the 'core' sound of them is pretty much the same. I describe it as a sort of Boogie dna (agedhorse may think that as idiotic). Every amp I have heard has had it.
My decision to go for the TT as opposed to a WD was very much down to those extra valves and fact that they had made a conscious decision to replicate the B400 tone stack. I'm very old fashioned in terms of the sound I want (I tell engineers to give me Bohemian Rhapsody). I fell in love with the sound of my B400 and 2x15s in 1988 and have not ever changed (other than to buy lighter Boogie stuff).
The picture shows that journey and comes from a session in a rehearsal studio when I took the two rigs in for a comparison. My ears didn't really detect any great difference between the two 'big' rigs. There are obvious differences (graphic eq and parametric) but that basic sound was there. I believe that the TT is going to carry that journey on without any marked change in the sound.
I will do the same when the TT arrives and hope that I'm right.