While I can not comment on the hitch extensions.. I can on what are called Anti-Rattle clamps for said hitch (By the way, I recommend at least one of these with your bike rack)
I got a "knock off" one.. which broke almost before I could tighten it down.
I have a genuine BLUE OX designed one.. I don't think I could break it if I tried.
That is one difference.. Blue Ox towing adapters are top quality, (So by the way is Roadmaster) BUT with the Google product you do not know what you got till it arrives.
So, what's the difference between the blue ox anti-rattle and the knock off.
Well, the knockoff relies on the strength of a weld, that broke
The Blue Ox either has no weld, or the weld is under compression (They do not fail under compression) (As I recall there is a strip of metal welded to the plate.. Given it's location if you stuck it on with model airplane cement it would be more than strong enough)
If you go with the low-cost unit.. Pay very close attention to the welds.
NOTE: This does not mean the Google product is bad.. Only that you need to pay close attention.. Sometimes the price is low because someone ordered 100 when he wanted 10, or 1000 when he wanted 100. And having thus gone belly up, a liquaditor got his stock for cents on the dollar and is passing on the savings.
Home is where I park it!