I get a pretty much identical Marshall sound from my Bluguitar Amp1 which is a tad smaller and lighter than a regular sized lap-top. It makes Class D bass amps look large, cumbersome and heavy.
In my old band the guitarist had one of these as a backup and A/B`d against his JCM900 the only difference we could hear was in the controlled feedback, the JCM performing more nicely on this aspect.
I love the Marshall sound, but I`m at a point where I can`t even lift a Marshall valve amp head, let alone carry one. Thankfully other brands can give the sound I want, just a shame that Marshall themselves haven`t developed something similar.