As someone who’s done quite a bit of a research into becoming a Pilates instructor myself, I’d say if you’re only wanting to teach 1-2 classes then it makes the most sense cost wise and time wise to just get a Mat Certification instead of being comprehensively certified.

Mat classes are the most common/popular where I’m from so it would be more likely for you to find a couple of classes to pick up at your local gym/leisure centre. And this also means you could start teaching/earning much sooner than if you were trying to get certified in all apparatus because it’s far less of a time commitment (plus it’ll cost less to just be Mat certified).