Looking at the hardware and knowing how much a non-magnetic 8’ x 4’ glass whiteboard weighs, I would not feel comfortable with using 4 plastic drywall anchors to hold it up. Maybe, if you had a couple going straight into a stud. Reviews seem to be mixed between magnetic and non-magnetic and this is listed as being non-magnetic. I was going to suggest to my girlfriend to put up at work, but going to pass.
I would not worry about the hangers. I have installed these before and four hangers in the wall are plenty strong enough.
The thing I would watch out for is either making sure you DO NOT hit a stud wall if you are not wanting to attach the board to the stud wall. love this style of dry erase board!!!
I just hung a 30"x18" one that I wouldn’t have trusted this board’s hardware for, much less 4’x3’. To each their own.