If it has the metal siderods its a good one, if it has plastic siderods then they could go wonky at any time. The very earliest ones were the ones most prone to this. If you can get the 1:22.5 one with metal siderods, that’s the best one IMO. It has a pivoting front axle that runs better on rough track, the later 1/20.3 version eliminated this in favor of more room for internal electronics and is more prone to derailment on rough track as a result, also the 1/22.5 is about 15% smaller than the 1/20.3 version so it works and looks far better on small diameter curves.
My main concern on a 30" diameter curve will be couplers, these are fairly long for a small engine, that means overhang ALOT of overhang on 30" diameters. I dont use this engine on the pizza because it has so much overhang it jams into the scenery. But if you use the knuckle coupler, even though it pivots, it may still drag the trailing car off the rails due to the overhang putting the coupler so far out of line of the track center. If you use the 1/20 version your guaranteed to have issues with this on 30".
I prefer much smaller engines for 30" diameter. I use HLW Macks and 0-4-0s, LGB Porters and Bachmann Lil Big Haulers, also I use link/pin couplers with extended length links to compensate for the tightness of the curves. The biggest issue with couplers is too closely mounted and the corners of the cars will bang into each other on curves derailing the lot. You should be OK with Bachmann type knuckles on small cars but you may have to do a bit of experimentation on the layout to see what works best mounting wise.