I've had them on my '09 JKUR since '10. They work great, are very robust. They are sensitive to setup, tolerating no bearing end play whatsoever. I chewed up a set of spindles learning this the hard way. The handling difference between locked in and unlocked is a revelation, and there is a mileage gain as well. With 37" MTR/Ks on TR beadlocks I get about 16 around town, 18 on the highway. They've endured many trips to Moab, Mt Blanca a few times, Chinaman's Gulch etc. and total carnage has been one broken lock ring. I may upgrade the hubs to Yukons some day but for now I run them with Synergy's RCV 911 inner gears and they seem to be tough as nails. Spyntecs are essentially CJ 30 spline Warn Premium hubs on proprietary hubs & spindles. Seals aren't off the shelf automotive stuff, so good to lay in a few sets for servicing.
So, are they worth the upgrade? Yes, IF you do so at the beginning of your build. At the time I built the rig angle corrected housings weren't yet available and I had a bad front DL vibe issue. So, I ended up getting a second set of wheels for the bolt pattern change. I also had to drop down a size in front inner shafts, but got chromolys and CTM U-joints, which have gone everywhere without complaint. I later found out RCV will make a set for Spyntecs, so if I break these that's how I'll go.
All that said, as I've mentioned in other threads had I to do over again I wouldn't put a penny into the stock front JK axle housing. I'd just get a corrected Pro Rock or Tera 44 and be done with it.
'09 JKRU. 4" Teraflex long arm, Teraflex R44 housing, Teraflex / Fox Resis, Poly Performance skids, Nemesis Billy Rockers, Nemesis flares, 37" ATZ P3s on 17" 5x5.5" Trailready HDs, Spyntec hubs, Teraflex BBK, Mopar BBK master/booster, Superior front & Alloy USA rear axle shafts, CTMs, Reids, Synergy drag link & tie rod, WTOR hydro-boosted steering, 5.38s, TF Dual Rate front bar, TF bumpers, Warn Powerplant, Tom Woods shafts, AA xfer case cable, Kilby canister relo, RH4x4 cage.