If you use at my site you would need UKPSF insurance and you'd get away with A5 but not an Ego unless your group was big enough to play alone and rest your group were happy you used it. Even then it would need capped at same rate of fire as site markers and have to pass the chrono speeds.
If you contact Go Ballistic direct I am pretty sure they state "no" as a general rule, but like my site we do take markers with certain terms. You will find with Go Ballistic they are pretty happy to try and make everyone who plays happy. But they take safety as a must over everything, so if that means another punter is going to be used as target practise by you then they will stop it.