Thanks to all for replies and comments. My conclusion from all of this
is that they are apparently fast, easier to use, and in some situations
vastly superior where combustibles or very tight work areas limit
access.

I used a Sharkbite fitting inside a wall when replacing a frost free
outdoor spigot.
It was a tight spot. A local plumber who replaced my boiler a few years
ago recommended
it as an easy and reliable solution for homeowner repairs.