I bought the combo version of the HT5 and think it's great, I've had no problems with it and for the money I think it's the best sounding amp you can buy. Sure it's not the same as a Cornford, Orange Tiny Terror, Laney Lionheart, Peavey Mini Colossal etc but it's class AB not class A like most other 5W amps (so a bit more power), Also it's way better than the 5W Epiphones, Fenders, Gibsons and Harley Bentons out there.
Does it sound exactly like a Plexi or Bassman? I don't think so, not perfectly, I'd say it's more JCM800 than Plexi but if you think of it as having a nice useable sound that can lean towards a more marshally sound or more fendery sound. It does a fair approximation, IMO the Marshally sounds are closer than the Fendery sounds though.
As for cleans, I'd say they're useable but there's not a lot of headroom. I'm not really bothered by this as I like a little breakup in my cleans (sounds, not underwear 8) ).
It really does sound great for the price and beats my old Valvestate hands down for practice/bedroom playing. If I had one complaint I'd say it's a little more bassy than I'd expected but it can be controlled with the EQ.