Yeeah agree with all said above.......I have flown virtually every FMS, avionics set up, there is & would have to say Pro line 21 is as good as they come.
There are a few gottcha's, best advice is to keep it simple, make sure the FMS is doing what you want it to!! build up slowly and really get to understand the FMS logic.
That is the key, any fool can press buttons in a sophiscated box when things are going well, but what happens when a couple of non standard things occur, and you start to get a little behind the aircraft, the good thing is with the P21 that the displays are so clear that your choice is displayed to you on the MFD as dashed lines before you execute it! Just take a few seconds to check that is the command you want....
Also has 1xxxx1 says it does sometimes not auto couple, I found the best thing to do is set up PNF's PFD inbound course prior to intercept, ready with frequency already tuned. (Depending on SOP's).
Again look at your FMA's..........if APPR FMS1 displays & you want APPR VOR1 make sure you know the difference between them, whats gone wrong & importantly HOW TO CORRECT IT!!
Fanastice bit of kit & when it is understood & used correctly it makes it a lot easier.