I went to Destination Star Trek in London in 2021. Overall it was a fun enough experience - saw a few interesting talks, met a few of the cast. Even though I ended up spending money I probably wouldn't have spent in a cooler-headed moment, my memories of the day itself were fairly positive as a one-off experience.
But it ended up leaving a nasty aftertaste for me. Most of the Discovery cast were there and they were promoting season 4 pretty hard (which was due to premiere the following week), but then a couple of days later CBS pulled Discovery from Netflix and announced it would now solely air on Paramount+, a service which was yet to launch in the UK at that time... I don't blame the Disco cast (whose social media reaction suggests they were as surprised as the rest of us) but it did make me feel like the franchise collectively had cashed in on UK fans' enthusiasm and then told us to fuck off.