I have one at one wash. It's 15 years old and still working. The bottom row of items is vulnerable to theft. I'm in a good area so it's not too big a deal. I keep waiting for it to die so I have a good excuse to replace it. I think it is too small, but the large ones are on the other end of the spectrum. Personally, I would not cut a hole in the wall to fill with used max vend II.
My view of vending is a lot like getnbusy's. If you have spare time and want to maximize revenue at a single site it is a way to increase site revenue, but you could argue that when you factor in cost of supplies, the almost inevitable shrinkage, and time required to stock it is probably the worst ROI on the property. I used to have a large refrigerated in the wall vendor and sold a decent amount of drinks in the Summer, but the unit not only uses a decent amount of electricity in the Summer, but heated up my climate controlled equipment room, so in addition to item cost there is a energy cost to consider (for the refrigerated units).