I'm a fan. Haven't had the II but the MK50 I had was a very responsive amp. Reminds me a lot of the SLO, but with a lower mid voicing. I don't need any more amps, but if I saw one of those at a good price, I'd probably grab it.
Can't really think of any cons to be honest. Great tone and feel.
No cons, just tone. A pity they are so expensive in the US. Over here in Europe (esp. UK) you can get them at great prices.
It's just an amazing amp with tons of tone. Don't expect extreme metal or anything, it's a rock amp that can do great 80s metal, too, loads of gain and stays tight if you set it that way. But IMO it's not really the best amp for the brootals.
I got an Mk50H and played a MK50II in the shop. I didn't hear any difference although many people say the Mk50H would sound better. Trick is to keep the channel volume on the drive channel up, so it basically works the same as the Mk50. This works great in balance if you like your cleans a bit dirty. Otherwise you have to work the Ch2 volume and might lose a tad of punch there.
Only downside is that it's hard to reach people at Cornford these days. But if you're in the US you deal with Wally (http://www.cornfordusa.com/) - he is a great guy and will bend over backwards to make sure you're happy with your amp.
I have been through a spell of amp changing in the last couple of years..Splawn Quickrod-Dual Rec-Blackstar series 1 100 head-Axe-fx standard-and now the MK50,best of the bunch for me!