I can't speak for "hmrr" but I've used airpods everywhere: NYC subways, London underground, Bangkok's MRT, airports everywhere, and I never had an issue with them connecting. I was initially surprised when friends of mine gave me a similar claim because prior to them I had extremely bad experience with connecting or partial-connecting to devices, but they really do work that well. If yours don't, I'd expect a defect worth an exchange.

But I don't think it's just Apple's airpods either: Most of the newer bluetooth headphones work and connect almost instantly with my iPhone; I have some Bose QC35 that I can report the same speed of connection of the airpods -- maybe even a little faster. I suspect it's related to some extremely modern bluetooth version or feature-set that might be difficult to discern from the box, but I have not dug into it deeper.

This being said, my airpods sit on my desk next to my Jabra DECT headset: Bluetooth is only almost instant, but DECT is actually instant. I first saw them visiting a cell centre (inside-sales team) team in Seattle, and so I asked about them and learned "we wear this thing making cold calls sometimes every few minutes, all day long, and it doesn't suck" and that pitch sold it for me. I wish it traveled better, because if anything rings (phone, skype, teams, zoom, slack), I pick up the headset and it answers on the computer at the same time, and I'd love (somehow) to have that experience when everything is packed in my rucksack.

I regularly zip in and out of London UK at rush hour on trains and tubes rammed with people with wireless earbuds, mostly AirPods. No problems.

As stated the only time I had a problem was standing next to an extremely large diesel backup generator which was probably RFI related.