The new ones (mk2) are slightly improved over the old ones, but it's mostly minor tweaks. They appear to be well put together and I seldom see anyone with any issues on any of the forums including the Daystate Owners Club. I'd also go as far as to say they are a good looking rifle, but without the electronics of the other Daystates, or a descent regulator, I think they are over priced for what they are.
As for accuracy, all PCPs of a certain quality will give you excellent accuracy with the right pellet, but they all vary model to model. I've had at least half a dozen MK4is's over the years and they have all been great, and would all give one hole groups at 30/35m - but some were better than others
James