All good advice here:smileup:.I've personally seen the little one get ripped off of vehicles and I've had the frame mounts break off as well (bad bolts to the frame from original installer). When it comes to reliability, I like grade 8 bolts to the frame with locking hardware. The small one goes to the bumper supports and the bumper itself (I don't remember if the bolts remained exposed or not though). Not ideal in my opinion.
The price difference doesn't look to be that great between the two on the etrailer website. I would recommend the frame mount just for the off chance you get stuck off road in the future and that's where the recovery vehicle wants to hook to. Would you really trust that bumper mount to fully support your vehicle without damage? The frame mounts have typical safety factors of 1.5 or greater, so even a class 3 frame unit will support a regular cab pickup that is fully loaded.
The 600/6000 seems overrated to me on the bumper only unit. I can believe it for the frame mount and you would be less likely to rip a properly mounted frame mount off the vehicle if it was stuck once it is properly installed.
You never know if you are going to get stuck and need a pull, nor need to pull someone else out. I've seen too many bent bumpers or bad hitches from improper towing techniques to recommend the bumper only mount.
Ultimately it is your decision, I can only suggest that you think ahead for what could occur and plan accordingly.
Good luck with the purchase and install.
Just like riding a motorcycle, You dress for the accident, not the ride. It's better be prepared and have more than you need, then not enough when you need it the most.