I’ve used it in non UST Mountain Kings for ages. At first the new tyres drink up a bit of sealant as the sidewalls seal – for a couple of weeks every time I got the bike out of the shed the tyres were near flat. The trick is to store the bike upside down during this sealing up period. That way if a tyre does drop to 5 psi (say) it doesn’t get squooshed and break the seal on the rim. Just pump them up before you sit the bike back on its wheels for a ride.
You might find it easier to get the first fitting seal if you run the new tyres tubed for a while – that way the beads get stretched to fit the rim. Otherwise it can be nearly impossible, even with a compressor.