IME, a single S15D will blow away the Walkabout in terms of sheer volume. Add a 2nd S15D and you're talking about competing with much larger cabs. I've heard more than a few people say that a Bag End stack is louder than a Berg NV610.
The Walkabout is a great amp, don't get me wrong. Just don't expect to get more volume from it. I can use mine for band practice and really small gigs, but it would get buried in any other environment of mine.
Tone is a different story. The Walkabout cab and Bag End sound nothing alike.
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