I think all hitch extensions are a bad idea. It doesn't matter how strong and sturdy they are, you can't change physics. Moving the hitch point further back behind the axle is bad. Period.
I stretched the tongue of my trailer so it can clear the camper and hitch up right behind the truck.
Nothing can be better than that.
If you only need 18" and aren't towing really heavy, you'll be OK with an extension.
Most of the guys here have a strict by-the-book mentality and use extensions because that's what the dealers sell. They're made in a factory and the numbers say they will work. And they WILL work.
But not as well as keeping the hitch point as close to the rear axle as possible.