I have been to one of these lessons and I liked what I saw but I think if you come up against someone who is good at Martial Arts you would be in a spot of bother.
The instructor asked if I had a Martial Arts background so I told him I did Muay Thai and Boxing so he said see if you can land a shot on one of my pupils. I dummied a jab which he reacted to then landed a low kick to his thigh, I did not bother putting much power in but it caught him completely off guard and had I put some power in he'd more than likely be on the floor.
I was then instructed to limit the attacks to punches and the guy managed to block them all but at times I was close enough to have been able to knee him hard in the ribs or get him in the clinch, obviously I did not as it was a 'play fight'.
I will probably go back as the idea of defending against knife carrying thugs and multiple opponents is something I cannot practice in Muay Thai or Boxing.
But having said that the guy blocked some fast punches so if you are looking for something purely for self defence that would help you out in the majority of situations I'd give it a go, just don't annoy Thai Boxers