How are you finding compatibility,
Compatibility is pretty good, but IMO not quite up to the compatibility that the V1200 has, but it will definitely get there.
speed and frequency of firmware updates?
It can vary, sometimes updates will come out every few days, or sometimes it can be a few weeks, depending on what they're working on. At the moment they seem to be working on something big so it has taken a little while.
Do classic screen modes get outputted through the HDMI port yet?
For the V4's, including the Icedrake, yes.
