Take your time selecting your instructor. I teach NACD and TDI full cave classes and I can issue a PADI Cavern card as well. I do not make any difference in my training when doing a PADI cert or NACD or TDI as I teach to the highest standard. The card given you in a cavern or any cave class is not a signature of certification as much as it is a recognition of training completed to a instructors satisfaction. If the instructor teachs you well regardless of agency then you will survive. The instructor not the agency is what to look for. Now if you were to ask me would I accept a PADI cavern for continuing education I would tell you that it would depend on an evaluation of your skills and knowledge both in the water and on land. I would evaluate any student regardless of who trained them and what agency they where trained under. I would also still go over the cavern fundamentals and skills as if they didn't have any cavern training. In short you could say I would assume you were not trained unless I trained you. That is the way we are in cave country. Good Luck and dive safe