Apple watch & Mint Mobile

Watch do not have SIM, i presume you mean eSIM,

The watch plan must be the same cellular plan as the paired iphone, unless set up as a family member (eg kid)

The plan must support Watch and MVNOs rarely do.

If you use the watch as though it was gps-only you can use whatever provider you want on the phone. Mint is fine. It will make calls provided the phone is in your pocket

You only need be picky if you want the plan also on the watch standalone.

If you mean will the cellular watch work as a non-cellular gps-only one then yes. Turn off cellular in watch settings. It can still make calls if the iphone is within range

Visible wireless (by Verizon) is currently the only prepaid wireless carrier in the US that currently offers a stand-alone wireless (LTE) plan for their customers. They allow you to add an Apple Watch LTE to your wireless plan for $5.00 per month. This allows you to leave your phone behind and still be able to make and receive calls, texts and use data on your LTE Apple Watch. -Hope this helps! 

[Edited by Moderator]

FStClair wrote:

This allows you to leave your phone behind and still be able to make and receive calls, texts and use data on your LTE Apple Watch. -

...in a limited way, third party email may not work, no whatsapp, snapchat etc and no usable browser.

I would assume its for emergency phone calls and Maps, and make a decision if the extra money is really worth it.

Apple Watch - Carriers - Apple