I responded below with my experience but have more information. I have a Windows (UGH) machine that it runs on well. Two comments here. On the Windows machine the app is running in 64 bit mode while on the Mac it is 32 bit. This is not the bigeest issuem but probably related.
The real problem is that this is not running directly on the Mac. According to Fidelity it runs on Crossover - which per Fidelity is is a version of Wine that is required to run Windows applications on the Mac. Wine is a compatibility layer capable of running Windows applications. However apparently not well and the combined app does a poor job.
As an example I added a second display off my iMac that was 1080 hoping that this might help. When I moved apps over there they were fine with the expception of ATP which was visible but not functioning.
Good luck but I doubt it will work well - this is not an app ported to the Mac.
Fidelity used to have a browser version but when they fixed all the problems they gave us this. Schwabb still runs in a browser on a Mac TD Ameritrade has an app but I dont know how good it is.