It looks like this thread has morphed from being about the retail environment to a "why would a newbie buy gear for a sport he knows nothing about."
I'm in this situation. I'd rather use my own gear while I am training. It makes no sense to me to train on gear I don't intend to use after I'm trained.
For example, the gear I purchased has a secondary air source in the inflator. I'd like to learn using this secondary air source rather than a traditional octopus.
It's possible I've bought all the wrong stuff, but I doubt it. If I have, you can look forward to some killer deals in the classified section.
You can do whatever you want with the good advise written here. You could buy all the gear you want. Vendors will be satisfied. If you dislike something in the near future, you can publish it here and we will get a nice bargain.
However I would not discard all the good advise written here.
I, as instructor, do not see with good eyes if an OWD student comes to my class with his own scuba gear (I mean BCD and regset). For the reasons written here, but also because I give the same gear to all my students, so the same explanation is good for all. If a student has something disimilar I must spend time with this student and the rest explaining the differences and additions. I do not know if the gear that the student has works ok. Perhaps yes, perhaps no. I would not like the added risk.
A different gear adds distraction to the rest.
Perhaps is just me.
I remember a student that came the last pool session with an Axiom i3 BCD. She just have bought it in a dive store. She didn't know how to use it. Our regs do not have the required BCD hose lenght. All what we have explained about ascending, how to release BCD air during ascend, etc was useless with that BCD. The moral of that session was keep that BCD for your dives and take the pool session with our gear.
Some months later she sold that BCD and bought a "normal" BCD. That was a misinformed purchase.
Furthermore, Integrated octo in the inflator is something that the COVID pandemic has killed. The reason is that if you need to share air with your buddy, you must give the main second and use the integrated octo. With the pandemic, this is no longer "proper" and scuba agencies are advising against. You can use it in your dives, but your instructor could perhaps not allow you to use it in the class.