The value for shiftmates is if you like the mechanism of Campagnolo 10, but want a wider range cassette (Campy 10 only ever supported 29 or 30T big cogs). A Jtek shiftmate allowed you to use Campagnolo everything but the RD and cassette, so you could get the lovely ultrashift mechanism, but use a 34T big gear in the back. Since 11 speed cassettes were spaced the same it wasn't an issue and 12 (and 13-speed Ekar) Campagnolo allows for larger big cogs, so it's not such an issue.