What's the latest opinion of risking a V3 to V4 firmware upgrade on this series of Hikvision NVRs, just not worth the risk?
It depends on whether you normally use the web GUI, or the VGA/HDMI interface.
The much-touted-by-Hikvision V4.x VGA/HDMI interface is totally different, and arguably an improvement over the V3.x version.
The web GUI isn't much changed.
It's fair to say that the new V4.x firmware is a bit flakey, each of the many versions has its own quirks.
But there are also upgrade risks, sufficient that Hikvision actually published an advisory on how to upgrade, attached, due to the many customers that were caught out.
If you don't follow this - you may end up with a corrupted configuration, and an inability to log on, and the need to perform some recovery actions.