I tried it out as a standalone app and I've got to say it sounds pretty good. Easy on the CPU and RAM and the latency is not bad. Not great but not bad. Certainly could hold it own with most apps and vst's on the market, tonally speaking. The IR's worked flawlessly but it doesn't like 32bit samples or any IR with over 20000 samples. That cuts out about have of my IR cabs and would definitely be pushing it for good quality studio reverb. Since I'm using the trial version I'm sure there is limitations so I need to go back to the website and see what is included in the full version but......
In the trial version I could not import any vst effects, there is no record or loop option, and there is nowhere to get at the effects. You can only pick presets. The tone is good but there are better free options online as vst's. With VstHost or LiveProfessor and some free amp sims such as AcmeBarGig, Aradaz, and Poulin and studio gear by Modern, Cabinet modeling with TribeIR or Reverb modeling with CatharsisIR.
Before you shell out the cash for this one... Check out some of the other standalones... Plektron Guitar Amp, Peavey Revalver MkIII, Kaussa AmplifikationCreme, and of course the one I can never think of by Native Instruments... darn!!! Oh.... Guitar Rig.
I have tried and used them all for recording, for practice, but none of them are really good for live use. The only one close in the software game is the Digi Eleven rack unit which is a hardware rack unit sporting vst plugins. But the price is steeeep!
Live Professor is meant to be used live but is still in beta. And has no hardware interface.