The x30 has better mid range than the Leopard. There are tracks where that makes it better, but also tracks where it is worse. The x30 does have a nice counterbalance that makes it a smoother running engine, but there isn’t anything else really remarkable about it, good or bad. It just makes its power in the middle, vs the Leopard making it on the bottom and top ends.
SKUSA hasn’t adopted it yet, but then its fairly new to the American karting scene. Since IAME is pushing very hard to stop producing the Leopard and wants everyone to switch to the X30, I could see it being more accepted in the future.