Comparing amps is difficult......if the difference isn't night & day, then there's plenty of room for us to convince ourselves of something based on our own pre-conceptions.
My Cello Duet 350 is a very good amp, so i wasn't expecting a big difference.
Sooo, i think that the Hypex has lower distortion, better control, more definition. At first i thought it seemed a bit dull compared to the Cello, but i think that could be lack of high frequency distortion. Anyway, as soon as i can get some cases made the Cello is gone.