Will a USB VGA Video Adapter Work on MacBook Pro (15-inch, Mid 2012)
Yes, it will work.  There's no reason it shouldn't.  But, You have a Mid 2012 which has a Thunderbolt port which is compatible with mini Display Port (mDP).  

Why not use an Apple Mini DisplayPort to VGA Adapter?



This will be going from a digital video signal to an analog video signal.  It's just my opinion that going from video to video is better than going from USB to video.

As far as "worrying" about whether it will work or not work, if you buy from a reputable seller like Amazon, or even eBay with their "Buyer Protection" you shouldn't have to worry that your item won't work.