I am perfectly ready to believe that the UL does not pull products off the market as quickly as they might. Especially in this case, where it is much more a matter of reliability than it is safety.
If anyone asks me, back stabs are worthless. They are part of the CHEAP design where the yolk does not cross behind the entire receptacle.
I simply will not use them. The stuff I use has a yolk that wraps all the way around the back of the receptacle such that the stress of plugging in the vacuum cleaner is fully supported physically. And the electrical connections can be torqued down such that you KNOW it is never coming apart. And without forming a loop, so I am not loosing all that much time. I don't wire whole apartment complexes, I'm not looking to trim five seconds off every last operation.
The fact that the UL is permissive of such limp equipment does not persuade me to use it. That is my opinion. Period. Ask me again? backstabs are worthless.