I had a relative who invested in them. He was advised to go slow. Get one see how it goes. But he decided to go head first and bought multiple units. He ended up losing $30k.
So my advice is just that: take a shot with one unit and see what happens.
You have to think that the better routes are already taken. Why would a company sell you a profitable vending machine route instead of owning it themselves?
I would guess most are not profitable.