The only difference between the Wurth gun and the Harbor Freight gun is that the Wurth gun (is expensive) screws onto a bottle of SKS and has a fancy coated handle whereas the Harbor Freight unit does not screw onto the SKS bottle and is plain aluminum. You have to buy a separate plastic bottle, pour in the SKS and shoot. I've used it, it works the same and the finish is the same assuming you know how to play with air pressure settings etc.... Having to buy the separate bottle is a pain but it was cheap (eastwood sells them). I choose to pay the $7 instead of teh $60 for the Wurth gun. SKS cleans up with water so cleaning the bottle isn't a big deal compared with the 3M undercoat which is a solvent base and a fiasco to cleanup (not to mention that you can't paint over it).

Now, having said that, please understand that Wurth also makes a different (more expensive) undercoat gun that includes features of a standard paint gun. It has controls for atomization and fan size. I believe this may be the unit originally mentioned at the start of this post. It's quite pricy and since most shops don't use them I just went with the cheap unit.

SKS works fine for mid 70 and later cars but the earlier cars were undercoated with patroleum products that were completely different materials and are harder to reproduce texture wise.

$.02

K-