I thought they'd be pretty much the same amp but not really at all. Good or bad is TBD but it definitely sounds different than my 40c thats for sure. One good thing so far is way less hiss on the ultra channel than the 40c. I have owned 2 40c's and both had the same hiss when the gain was past noon on the dial. The reverb on this DSL20HR is much more pronounced than the 40c which is eh whatever, I don't use much reverb when I do actually use it so I liked the reverb on the 40c. The 20HR seems to have more gain on tap on the ultra channel while no crunch mode on the classic channel. That works for me considering this amp is pretty much intended to be used in a classic metal tribute so there aren't a whole of in between sounds needed. I can get the classic channel to break up some by diming the volume and controlling overall channel volume with the gain knob so it's all good.
Overall happy so far because I wanted a Marshall in head form and these DSL's deliver the goods if you take the time to learn how to dial them.