I guess pure foot pedal machines are harder to find. I looked through the local ads yesterday after reading your wanted post and could not find one.
ACS is really nice when it works right. Since it's introduction, every customer has been a Beta-tester, and bobcat's been working the bugs out ever since.
When you think about the basic Bobcat system, ACS is not really that much more. I mean, if you have a newer foot pedal machine it already has a controller, various sensors and miles of harness anyway.
I don't know of anyone who owns an ACS machine with any hours on it who has not had a malfunction, but I imagine there must be owners out there who never have.
The most common component to fail is the actuator. Like I said about the Beta-testing thing, the most current actuator is yellow-labelled, and requires a software update to run it. I have yet to replace a yellow-labelled actuator, so maybe they finally got it right. But they've only been going since early this year. Still, that's a longer run than the earlier ones.
If you're in a spending mode, and depending on what you're looking at and who you're buying from, perhaps you could haggle into the price the cost of updating to the yellow-labelled actuators, then get that done as soon as you made the sale. Just a suggestion.
I think you could rest easier with an ACS machine if it had the latest actuators, and waiting for actuators to fail before replacement might let you down when you need it most. I dunno tho, there's always the rule about if it ain't broke.......