Dan,
Other than Swarovski Optiks on-going R&D minuscule coating improvements, optical differences should be minimal and difficult, if not impossible, to see.
In the newest 3rd generation Field Pro model (#35210), some functions, cosmetics and ergonomics were addressed. The focuser now has a black, more tactical rubber feel to it, along with a locked-in diopter setting. The objective covers are permanently attached for ease and reliability of operation. The instruments rubber armor also has a more tactical feel, making single hand holding actions easier in more variable weather environments. The new 360deg locked in carrying strap attachment system is unique, supposedly offering versatility and convenience in length adjustments and reducing tangling straps.
Some love the "innovative operating improvements", others prefer the previous tried and true. I have two 2nd generation ELSVs (8x32 & 10X50) and have no need to -upgrade- to the FP (at this time). IMO, if you can find a great deal on the previous models, their optical prowess and superb performance would make them Great Buys!! :t:
Ted