Seems to be very little point in hanging on to a pro account.
The main reasons I went to pro was image size restrictions and upload limits.
The former is defo gone now and the latter appears to have gone but there is nothing explicitly stating it on the Flickr site but a couple of places have suggested there is no longer a monthly upload limit.
I don’t have an issue with the new UI.
As for Ads? Meh, doesn’t stop me using Faceache.