Germie,
As a cave instructor you may have spent some time in Northern Florida. When you ask there which instructor you should train with, you do not have to read much between the lines to find out who is considered competent or not in that community. Granted, nobody will claim there either that agency X is better than agency Y.
But the next time I am down there I could make a list of all cave instructors teaching there and I could solicit a peer vote. I could ask every instructor I run into to rate the other instructors on the list with either a thumbs up or thumbs down. Would you be surprised if there is one agency that would get very few if any thumbs down? (There may be an occasional comment "He is a demanding SOB" in that group though.)
So for the sake of peace let's agree that all agencies have great instructors but that there is at least one agency where you would be hard pressed to find a bad apple in their bushel. There are plenty of great apples in other agencies too but you can't just grab the first one. You need to pick and choose.
I am OK with solo diving. Trimix is great. Rebreathers are wonderful machines.
Solo rebreather dive with massive deco or hard overhead? No thanks, if there are other options.
Similarly, I have flown solo, single engine, in IFR conditions but I knew that I will be totally f***ed if the engine quits or the weather turns into serious hell. (A second engine does not make the weather better but twins have typically de-icing/anti-icing, better instruments, autopilot, etc.). I never pretended that this was a wise choice even after getting away with it.
When I was looking for a tech instructor, cave or trimix, I looked for what fits me. Begin with the end in mind means also take a course that helps you. In diving, and in work or with other hobbies. Nobody else can decide for you. The thing is that sidemount or ccr are/where no options with all agencies, so a way to say no for those. I was interested in this also.
So, on my list of instructors where all extreme experienced divers who do ccr and sidemount also.
Not that others are bad, but not fitting my needs. So easy it can be. And happely you are free to choose. I know great instructors that have a thumb down for myself, just as explained because they dont fit my needs when taking a course. But I dove with some outside courses. And normally you have to do every course just once. No need to spent the time and money to do the same levels with every agency.
I dove in Florida with a lot of great divers and instructors from different agencies. But I did with only one instructor my course, one of the pioniers in cave, ccr and trimix. Tom Mount. With IANTD ( he teaches nacd and nss cds also).
Oh yes, the others were also good, but I could only choose one. So easy it was.
In Thailand was only tdi an option at that time, so I choosed my instructor not agency based. For full trimix it was an instructor advertising iantd. I contacted an utd instructor also, but wanted to do the course in Malta.
So there are other great options, not worser than others. But for some things not every agency or instructor can help you. Or you already have certain level and want to progress. From intro to cave to full cave? Normoxic to full trimix?
Cave with padi? Rebreather with every agency? Rebreather is unit specific, so for some you have to go to iart, iantd or tdi. Others can done with padi or iac also.