The firmware is the same between the original ST16 and the ST16 "Pro" version. The original had two antennas on the outside, one on the inside. The hardware is the same except the other antenna was moved outside to make it look like it has one more antenna. It doesn't.
Avoid mistakes?
Yeah. There are some mistakes that new folks often make. Some by doing. Some by NOT doing. Here are the biggies:
1.) Do a factory reset, create a new Model and bind to it. You have no idea what the previous owner has done to that controller. The previous owner might not even know. Do yourself a favor. Play it safe, clear out everything, and set the thing up as if it were a new controller.
2.) Channel Settings. The Channel settings were carried over from previous systems where the controller was purchased separately from the aircraft and had to be adaptable to an infinite number of aircraft. The ST16 flies the TH. That's all it flies. It's already set up to fly the TH, with no further need (OK, maybe some special cases. But that's a whole other thread.). The problem is this system is very easy to mess up. It is easy to change things without having any idea you even touched them. If you are not experienced in adjusting channel outputs, leave it alone. This is another area where the forum has a lot of sad history that did not need to happen. Channel settings can be turned off by disabling "Advanced Options" in the System Settings.
3.) Stay out of the "Hidden Menu" and especially the stick calibrations. That would be the third tale of woe related to big troubles caused by trying to do things that did not need to be done. The Hardware Monitor and the Final Output display will tell you if the sticks are working properly. If not, do the required maintenance. Do not try to calibrate around a maintenance issue.
4.) Firmware updates: The fourth tale of woe. Don't do them unless you have a need to do them. If the controller is working normally and doing everything you need it to do, leave it alone. This forum is loaded with sad stories of controllers that got bricked during failed updates. And most were being done just because they were available.