Freedom No-Pull Harness and Leash - Teal/Large 1"

We have been successfully using a Gentle Leader, but don't like explaining that it's not a muzzle. Is this a good alternative?

Is this harness easy to apply to the dog, or does a person need an engineering degree and a perfectly still dog to put it on?

Is this a harness that can be left on the dog all th time, or will the dog be able to chew it?

How to measure to get right size I see that seems to be the big thing. I want to do this right. Thanks for the help.