If this was truly 150 times more intense than a single session at the gym, wouldn't the strain on the body would most likely send you into shock, a coma, or even death after a couple days? Regardless of the efficiency, your body needs to exert 150 times more energy if you wish to gain 150 times the results.
So...I do this. It's not 150 times anything. I think it's probably 3 times more effective. So you pummel yourself dead in 20 minutes (basically to failure in all muscle groups) when it'd usually take an hour. And the other thing is you reach difficult muscle groups like lumbar which you might not normally be able to target. I like it. It's different and quick and effective.
It depends on the intesity that you trained. Maybe your trainer did not push you hard enough because he did not want you to be very very sore the next few days. Something like that might scare a person away from using it again. It depends on the person tho. When i first got trained, my whole body was sore for the next 4 days. My trainer really pushed me hard. I could feel the difference the very next day.