Wellll.... I approve of sites doing regular spot checks all through the day, using their own BBs, and heavy ones at that.
But.
If they're going to do that, they need to be absolutely clear about it so that you can tune for it, and provide them at pre-game chrono as well.
Mugging people with a surprise weight is a cad's trick. And it's a peculiar weight at that. If they're really concerned about what over-volumed guns can creep up to by loading heavier BBs, they should be using 0.4g or even heavier.
Sounds like another site owner who has formed a muddled but adamant opinion, and now won't be swayed by reason or logic. Sadly, there's no critical thinking test for running a site.
[EDIT] Oh, this lot? https://firstandonlyevents.co.uk/first-and-only-airsoft-rules/
I've ranted about that "actual" and "variance" utter gibberish before. What a bizarrely over-complicated way of saying that they have a 1.1J limit for AEGs[*], but 1J for HPA. And they explicitly say "All our Chronographs are measured with 0.2g ASG bbs", so why would you tune for anything else?
[*] Also, they don't seem to know that 350fps on 0.2g is 1.13J or 1.14J, not 1.1J, so it's not even clear which figure they'd use.
I'm calling Dunning-Kruger on that.