How necessary is a zerostat gun?

It all depends on whether you have a lot of static that builds up on your vinyl.

I don't, so I don't use the zerostat gun, even though I have one. (Or had one, as I think I gave it to a friend to try who did have a bit of a static problem.)

So in my case, the answer would be: Not at all.

My two cents worth.

I have one but rarely use it.

It helps but it isn't necessary unless you are living in a dusty environment like NYC.