Elbeinlaw

I would say: no question that the "do not use an adapter" is generated by someone's risk management folks. I mean, if you have a 2" receiver and need to use a less than 2" shank--which a user will any time there's a less-than-towing requirement--what choice is there? It's not like you can get a swiss-army-knife attachment (like some of those multi-ball-size attachments) that let you select what you need. So there isn't much question in my mind that "foreseeable misuse" trumps their risk management OCD-ness.

However, it is certainly true that the hitch mounted bike racks are already unstable--you have the weight of the bikes concentrated on those long crossbars that run parallel to the bumper, and when they bounce they torque the hitch's shank--and lengthening the shank is going to make it more unstable still. There's a lot of movement there, and I suppose it could easily get out of control. You said you have a trailer, so you know how this can happen.

I also have one of the tray hitch-mount bike racks. I love it. But the thing moves all over the place. The guy I bought this from convinced me to take the anti-movement fixture, which I didn't want. Maybe I should use it, but I don't. I don't see that it will actually help that much.

All that said, I've never seen the non-extender reducer. It will certainly address the size mismatch between receiver and shank. And maybe it will dampen movement, too. But I'd worry about it getting stuck. The shanks and receives rust like anything, and I'd hate to have that thing stuck in the receiver.

Is there an option to get a smaller receiver mounted to the front of the vehicle? Then you could use both sizes, no prob.