The Electric/Hydraulic kit is a true third function because it's a complete spool valve connected in series with the loader valve. Instead of having another lever, it's operated electrically. The valve itself mounts just below the existing loader valve on a WR Long supplied bracket.
The selector valve is also electrically operated but is connected to the work ports of one of the spools on the loader valve. It switches the function (usually curl) from the loader bucket to the grapple. The selector mounts on the loader arm near the bucket.
Ah, but there is a big difference. As I stated above the selector switches between a loader function and the grapple. The electric/hydraulic valve gives you another function which may be used simultaneously with the loader functions. This may not seem to matter much but it is a more flexible option and according to Nelson Long, is the most popular option.
WR Long does not sell direct. The prices quoted are MSRP. My local JD/WR Long dealer charged me MSRP and made his profit from that price. Your dealer's mileage may vary.
The kits contain just about everything you will need for a basic installation, hoses, fittings, mounting plate, valve. However, most people like to customize the installation a bit to suite their individual tastes and situations. I replaced the supplied hoses and fittings with a different setup so the disconnects were at the loader instead of the valve.
You are welcome to visit and inspect my installation.