I just finished installing Hellwig's BigWig rear sway bar and the regular Hellwig sway bar on the front of my 2008 F250. It made a bit of difference in the amount of sway on the first drive this afternoon on a winding back road. The ride was empty, I can't comment on handling when towing since we don't have a 5th wheel yet.
The factory front sway bar was almost the same size as the Hellwig front. However, the factory rear sway bar was tiny compared to the Hellwig.
Factory front 1.10" Hellwig replacement 1.25"
Factory rear 0.65" Hellwig BigWig 1.31"
Front sway bar was very easy. Reuses the same drop links and hardware. Only the bushings and brackets are replaced with the new sway bar. Probably an hour job.
The rear was a pain. The factory sway bar on my F250 was a wide bar, mounting at the shock mounts on the axle. The BigWig bar mounts over the differential and drive shaft and the brackets mount just near the differential housing at the axle tubes. I had to remove the passenger shock and parking brake cable bracket (at passenger shock). The bigger pain was removing the fuel tank skid plate and aft fuel tank mounting strap so I could move the tank an inch inboard to remove and replace the driver's side sway bar link at the frame. The tank is put back in place when finished of course, but it does add to the task.
If you order, check the hardware in the kits to ensure you have everything. I was shorted some 7/16" x 2 3/4" bolts and washers for the end links and had to make a trip to Fastenall. If I had been performing the install on a weekend, it would have been quite painful.
I don't know how much of a difference there is in the 2012 and 2008 models, but I hope this helps some.
OJ
Edit : The rear BigWig bar has 3 positions for the end links to increase the force exerted by the sway bar.