I recently attended the On-Track online seminar and thought it was very good. It's professionally run with relevant content and all the powerpoint presentations were available to download for a few days before to review the presentations. The number of attendees wasn't a concern, but on the second day we were split into 'breakout rooms' with maybe 8-10 attendees which allowed a bit more interaction. The presenters are all incredibly experienced in their field and no question was left unanswered even though we had just left the EU with all the associated changes etc.
I have no experience of FPT, but I wouldn't hesitate to use On-Track again. I hope that the online version will continue to be available when life returns to normal as it was much more convenient than a trip to Wellesbourne or wherever.