I leave it hanging near the bottom of my shirt so I can reach it anytime, but you could also bring it out the neckline or use the quick adjust on the lanyard to extend it below your shirt when you need access.

The cord on the back of your neck is the most uncomfortable part. As far as overheating, LDS underclothing is a much greater source of discomfort on a sweltering summer day.

Neck pouch may be overkill for some areas, but in places like Paris or Rome I find it worth the peace of mind. I've seen too many pickpockets who are skilled at targeting purses or backpacks even if they've been zipped up, or who watch people put away their wallet and then use stealth and/or diversion to reach into that pocket. A neck pouch complicates the process too much for them, and fits things like passports no problem.