How useful an engine like this is really depends on the availability of compressed air and electricity. It would likely be a lot quieter and cleaner than an internal combustion engine, but given how affordable and efficient electric motors are, you'd need a strong case not to just use one of those.
There's no rare-earth minerals in this engine though, which is a possible selling point in extreme resource constraint scenarios.
Ok, looks like I was a bit off on the compressor angle. It wouldn't take running it in reverse, it just requires offsetting the valves (in purple) by 180 in the cycle. If you have a mechanism that can do that, then the engine can switch into "regenerative" mode mid-operation. That's got a bit of potential for vehicles with regenerative braking.