what is the difference and how can I identify the two?

Having had an older SLC and compared to a brother-in-law's newer SLC, I can tell you the newer model had a more neutral color (less toward yellow) and better resolution. It was easy to tell the earlier one with winged eyecups from the new one with twist up eyecups. I'm not sure about how to tell the difference between the latest couple generations of SLC. A new one is on my long list of things to buy. Ward

The SLC Neu's are darker green than the "older" SLC's

Aside from the minor body design differences be aware that pre-neu SLCs from about 2003 on also have the Swarobrite coatings and thus perform optically identical to the neu version. Frankly I prefer the older body better and my SLCs have Swarobrite coatings so I feel I have the best of both worlds