New band for Fenix 5X?

I went through this thought process too. Conclusion I came to was "How much would it cost to replace the watch if the 'cheap' strap failed?"

Since heart rate doesn't work properly under water you should be using a chest strap for that, and if so, go with full Nato. Both waterproof and impossible to lose the watch. Replacing with quick straps are simple too, the Nato just slide under the lugs 

I have a "modified NATO" style on mine.  The pins are screw-in on these watches so the usual issue that a NATO strap solves (spring-loaded pins that can pop out) are a non-factor.  A full NATO style strap works but blocks the HR window.  I like my all-day readings.

I think I paid something like $10 for it; when it deteriorates (it's been fine for a year now) I'll just buy another one.... 

AliExpress if you can wait.

I got a cheap one off Amazon. Should hold me till the Fenix 6 comes out.

Exactly. You paid $500+ for the watch. There’s a reason why something is cheap. Just do it right the first time. 

i like the nylon ones more than the rubber https://www.amazon.de/dp/B07KTZMVGZ/ref=pe_3044161_189395811_TE_SCE_dp_1

All the cheap ones popped off my hand wrist; never happened with original Garmin bands. Don't do it!