Mana kaki-kaki Celcom sekalian?

It's not a question of Celcom vs Maxis but more importantly it's a question of which telco has the best coverage where you work, live and play. If both maxis and Celcom have good service and speeds in your area, then yeah, Celcom makes sense since maxis will not offer new iPhones on their 98 plan till few months after launch. I've tried all four big telcos and for me personally, maxis has been the better provider in terms of coverage where I move about and of the four I would say their customer service is probably the best for me - but that's subjective as different folks may have different experiences with various customer service officers. Anyways, point is, don't pick a telco for the device, but for the coverage.

Yes, please switch to Celcom. It is not worth being loyal to Maxis. Their line is not better than Celcom in most of Subang and KL area. No point to paying overpriced data. If you do a speedtest even Celcom is faster overall.

Hi bro, no, the iPhone 6S I bought was a used set, the owner replaced the battery before selling it to me. Now at 98% battery health

I preordered iPhone 13 pro max with celcom. Do they ship on the launch day or earlier so will get it on the launch day?

It is changeable but only at the service centres - or of course, you can DIY on older phones after the warranty has expired.

128GB should be sufficient for most normal uses. Enjoy the phone!