I recommend that you interview a couple of different instructors to find out what teaching techniques and philosophies they use in class and go from there. I personally would want to know from you, what your background is? Don't take offense, but just because you have a DM rating doesn't necessarily give background as far as other classes you have taken or the gear that you have experience in diving. Before people sign up for my Tec Class, they will do My Advanced Buoyancy Program that consists of a pool session and three dives a Dutch Springs. This program consists of Advanced finning techniques, Buoyancy & Trim, Air shares (long/short hose), redundant air system, SMB deployment with the most valuable part being Video Feedback. After each dive we will review film on TV and then build on that for the following dive.
Something like this will give you great feedback as to where you are truly at with your diving and if you are indeed ready to start Tec. I just had a guy (DM) this past weekend that was going to start tec and after taking this program has realized that he has to practice a little more before starting his Tec program.
Feel free to call me if you want to talk more in depth about this. I do all my training upon request.