I haven't played enough to say, but I took a look at several slow play tournaments (30 days + 1 day/move) on the Scheming Mind site. White won 141 games, Black 111, with 4 draws - and that gives White a percentage score of just under 56%, not much different from standard chess. So that gives some idea, but with the caveat that many of these players were inexperienced, and that many pairings will have been between players of widely different ability.
I hope to play a few games of Three Checks 960 later, thus dodging whatever opening theory has so far built up!
Does white have too much advantage in 3-check?
White does seem to have a bigger advantage in Three Checks than is perhaps desirable, and almost certainly a more significant advantage than in standard chess. One 'solution' is to play Three Checks 960 (if there's an opportunity) where most starting positions reduce White's advantage. See https://www.chess.com/forum/view/chess-variants/fischer960-3-check-evaluations-and-best-1st-moves - posts #3 and #4 especially.
I feel attracted to 3-check after playing a couple of live games. It's all about tempo, and counter-intuitive from the perspective of normal chess.
But because it is all about tempo, I feel that White has a considerable advantage.
What are the thoughts?