I wouldn't be too worried about using a demo binding under "normal" use.
I define normal use as 10 DIN or below, no cliff hucking or skiing where the binding needs to absorb huge hits, and also not being used for racing or other competition where things like weight and stack height come into play.
My wife and I scour demo fleets like vultures and have owned several skis with all kind of demos. We've never had a use problem with any of them.
As other have mentioned, there are downsides. They can be significantly heavier than other standard binding options. They will have some additional slop from the get-go and as they age the slop can be expected to get worse. They have more parts that can fail, which is why I would be hesitant to be doing high impact skiing on a demo binding.
But they have lots of benefits too, like being able to loan a pair of skis to a friend and being able to move the mount position forward and back without a remount.
I think MOST people skiing recreationally won't have any performance issued skiing a demo binding, and whether or not to use them is a personal choice.
My wife just purchased a demo pair of S7W, and this is the first ski that we had the shop keep the bindings and mount our own- the S7's were much longer than my wife's previous ski, and she was concerned about weight, so we had them take off the demo bindings to get the weight more in line with her previous ski (that was also ex-demo). But, if we didn't have a free pair of bindings around, we would have bought the ski with the demos and not worried about it.