Can't someone just order a bunch of tokens from one of these sites and then use them at any arcade? Assuming of course that the person bought both .900 and the .984 size tokens. Just use the size that fits the mechanism, right?
For this reason, I'd have no coins in my arcade. I'd use those card readers. Talk about no value. And people swipe those things left and right with no idea how much is on them. Plus, people will take them home and say, I'll use them another time, only to lose the card.
Also, no stealing by employees either. They can't steal quarters or sell tokens cheap to people (I'll give you $20 worth of tokens for $10 bucks), or simply give them to friends to play for free.
Any reason not to have card readers, other than maybe the initial set up costs?