Just for the record, now I'm back in terra firma Inglesia...
Web check in pro - it's very fast. I walked past all the queues. got my bag dropped off in a couple of minutes and was off. Took longer to buy a breakfast panini. Seat allocation worked fine. Same on return. The staff don't seem that experienced in managing it, though: on the way out, it took a moment for them to find a security person to check my passport and ask the 'did you pack your bags yourself?' question, and on the way back I had to be called back to the desk because the person who asked that question wasn't around and nobody had noticed.
Web check in con - the other chaps on my flight who took the old option and arrived at the last minute got upgraded. Gah! I suppose it's a question of whether you want to be guaranteed a good seat or... do you feel lucky, punk?
As for the IFE on VS19/20 - of course, I got the old system on the way out (when you want to stay awake) and the new one on the way back (when it's a good idea to get as much sleep as possible). And is it my imagination, or are the new configurations even tighter on the bum than the old? I could barely move...
R