Half inch in the tube is very common. I gain the same in the ADS, and at time, 1 full inch, after half hour of warmup stretching. I thought I went crazy at times, but once your tissues are suffiicient pre-stretched, the tissues will not fight back. It will relax. But for it to work within a few minutes, I can understand why with a massive rental price tag.
I already researched into the shockwave "vibration" therapy a few years ago. This is an old technology being incorporated to modern medical practices. Think about fat cell destruction through vibration/ultrasonic and cold treatment. It's been in practices since the early 1990s. The vibration system was incorporated since the 1960s through interesting gadgets.