It works fine. I have done it. The design of the Atlas turntable doesn't really rock at all when secured properly to the table. it was fun having my train stop short of the TT, uncouple the loco, put it away, and bring another out to connect to the train, the carry on. Prototypical, of course not, but neither is my layout or how I run my trains.
Anyway, the Atlas turntable will be fine on a main line.
Just make sure your approach tracks are level or shimmed up properly, and are as snug to the turn table as possible to have the smallest gap possible.