I'm on the fence about buying the 75 for P3D here and looking for help from knowledgeable 757iii owners. 

I bought XP11 and the FF757 thinking I might try something new and it ended up being a gigantic waste of money.  I'm leaving my current airline to start training for another airline where I'll be based on the 757 in real life.  I was hoping the FF757 would simulate the FMC well enough that I could accomplish non precision approaches with the use of VNAV, but unfortunately that aircraft only has the beautiful looks and not the brains.  With that being said, it's great for practicing flows, but not much else.  I'm really close to pulling the trigger on this 757,  but I want to know if the FMC is modeled well enough that I could say load half tanks and do about three or four non precision approaches (VORs, NDBs, RNP/RNAV, etc) with the use of LNAV/LOC/BCRS and VNAV.  Can anyone answer this question for me?  I know the CS website says the FMC features LNAV and VNAV etc.  I get it.  The other website said that too...

I've tried watching a few youtube videos out there of random CS757iii owners shooting approaches, but it seems most like to do an ILS which is 90% of the instrument approaches in real life, but training is a different story.  The approaches I have watched on youtube as well seem to omit whether or not the FMS LEGS page contains coded GP information for the approach loaded (i.e. I can't see any indication of a GP the aircraft will follow when VNAV will be engaged) which is usually right around the MAP or the RW_ _ waypoint.

For reference, I've been using another company's 737 with detailed FMS and Avionics interfacing to do exactly what I'm talking about now, but I'm hoping the CS757 can do that too so I can practice on the aircraft I'll be training on.

I appreciate any input.  :)

I’d say go for it. There are a few issues with the FMC that I’ve noticed (mainly on STARS), but I don’t think you’ll have any issues utilizing the CS 757 for your intended purpose. If you have any questions, feel free to PM, I’m a 757/767 captain with a US airline and would be happy to help if you need it. Congratulations and good luck with the new job!

Excellent.  Thanks for your response!