I think they are worth it! I pulled my fifthwheel only once without the mag-hytec installed. For whatever reason, paranoia I'm guessing! I was checking everything out after pulling my trailer. I had run my truck pretty dang hard and I put my hand on that rear differential and HS was it HOT! It would be neat to see the actual difference in temps between a stock cover and the hytec, but really you can't go wrong by getting one. Even if the fins didn't do squat (which I happen to think they do) just having the extra fluid capacity would make it worth while.
I'm also running the amsoil severe gear in the diffs. I think it was the 75W-110 or 140 this last time.
__________________
05' QCLB 4x4 NV5600,Spec DD clutch,S-06,5" TBE 6" aussie, airdog 150,modded fuel can.,CAI, techni-cooler,mag hytec rear diff. cover,6" lift on truck and fifthwheel,firestone airbags,16gal. of 200 PSI OBA 421HP/1009TQ moves 8000lbs to a 13.88@97.05
SSW