X97s sure are good shit. Obviously they're great on rough outdoors (asphalt, rough concrete) as mentioned here numerous times, but I've ridden them in my dusty local indoor (smooth concrete flat + plywood transitions) recently and the performance is solid. No problems powersliding on smooth concrete, doesn't slip out easily on plywood. Speed? Not quite up to par with F4 99s, but that should come as no surprise. A great all-around indoor park wheel if you want a bit a safer option as per F4s.
Having said that, if I want to go full gnar and have as much speed as possible at the said indoor, I still choose F4 99s at the risk of slipping out sometimes, as they undeniably are f*cking fast.
CAVEAT: still to try my new X99 55s at the same indoor. Very interested, will report back soon.