The event calendar is here:
Veri Calendar
Based on what I've done so far, the rides are not all that difficult, as they are catering to people on 30+ year old bikes getting out to enjoy themselves. It is targeted at having fun rather than being ultra competitive. Everyone is friendly and helpful, and they all appreciate the time and effort involved in restoring an older machine back to its glory.
Having said that, I personally ride them as hard as I can, and try to get the most laps that my body and bike will allow.
For me, it is a chance to ride a TT600 like I should have back when I had one in the 80's. Whilst I did the Blue Light and Eildon Nav rallies back then, they were still low key events compared to the proper enduro scene. I can now ride the TT a hell of a lot better than I did back then, and I am thoroughly enjoying doing these Vinduro events.