If you are in Los Angeles California you sould not pay more than 350.00 dollars for your Cert. All of the above is true. So sort it out. The instructor is the most important, along with the training in general. Take for example American Pro Divers who offer a 2 day course. You will be a 2 day diver, you really can absorb much info in two days unless you are in the military or parmailitary service. So with that said look at th provider and see where they are comming from if they endorse such activity then you can see where there motives lie. PADI has great program that can be Life Changing just study all the material PADI offers read every book and absorb as much as you can. Check out the NOAA diving Manual. It all depends on what you want out of diving if you just want to go to 40 feet and see fish then you don't need to understand dive physics. On the other hand if you want to be a Hyperbaric Nurse, then dig in and get to learning.