It will work exactly like background checks from gun dealers do. An individual sells a gun, a small fee is charged for the purchaser's background check. Will some ignore the law? yep. Will most responsible gun sellers follow the law? yep. No, it's not 100% effective, but it will make it much harder for a thug to get a gun. Our laws against robbing banks aren't 100% effective either, but they are still worthwhile.
...and irresponsible gun owners, like the druggies, gang bangers and thugs that use guns for most of the gun crime in the US, won't adhere to anything.
UBCs are absolutely worthless to stop a future crime.
Nothing more than worthless feel good bullshit from confused Liberals that deprive us of our Constitutional rights.
The agenda of the Left is not public safety. It never has been. The agenda is to take away the ability of the Right to oppose the Left's agenda to make this country a socialist shithole.