For the why not aspect:
-If they're good, aftermarket ones are generally garbage quality. I replaced my 300k mile ones with Anchor mounts and they're not bad, just not good. They have settled quite a bit in 20k miles, so they seem like they're starting to show signs of being worn and the inside vibrates a little at idle. I initially, there was zero interior vibrations, but slowly it has started happening and I'm not as big a fan as I was when I first put them on.
- The Brown Dog mounts are good QUALITY. However, they are solid. They'll shake your teeth out. Been there and done it, and I don't recommend them to anyone unless their rig is purely off-road.
-If you are ok with changing the mounts every few years, then the cheapo anchor mounts are fine. I think I paid like $6 for them on Rock Auto. They're easy enough to change, so I'll probably be putting another set on soon. Of you don't want to do that job again for another 20 years, buy them from Jeep.