I have been an open water diver, trained by YMCA and PADI for 25 years, have well over a thousand dives (stopped counting a long time ago, probably more that 2.5k actually) with several hundred of them being in the 170 to 200 foot range, several hundred being decompression dives with absolutely ZERO incidents. I have done penetration dives in what would be considered very advanced diving conditions and again have had no formal training beyond the basics. I learned by trial and error, watching and listening to those who were more skilled than I, reading everything I could, and understanding the physics and physiological effects that this kind of diving has, just as many of the great divers of the 70’s, 80’s, and 90’s learned. The only reason I have recently begun to look into more advanced certifications is because we live in a litigious society and now I need these certifications to go on trips to make dives and to get the mixes I want, heaven forbid we can all dive like adults within our own comfort levels.
That said, I find myself tired of people taking the “high road” saying oh I wouldn’t want to dive with you because TEC divers only dive for a reason or for a mission…blah blah. Well, if that’s so, I feel bad for you if that’s the only reason you dive. I dive because I love it and there is so much to see, so much so that I will never be able to see it all in my life, I dive for the thrill of discovery, and the excitement of seeing something new that I haven’t seen. This is so whether it is TEC or REC, I dive to discover and be amazed by what I see. We all should, too many people get caught up in the philosophy espoused by their various agencies and forget that we learned to dive and continue to do so because it’s fun.
That said, as long as you are safe, have the right gear that makes YOU and the people you dive with safe, and are happy with the manner in which you do it, I don’t think anything else matters. This segues into my answer to your original question, the agency really does not matter, it’s finding an instructor that understands you and why you want to make more advanced dives, is safe about it, and holds you to a standard that will improve you as a diver. Any one of the agencies will fit you just fine to advance your skills, since at the end you are only as good as you make yourself by learning, understanding, and practicing the skills you need to safely dive your profiles as you choose to do so.