The outside diameter of PEX is controlled, but the inside is smaller than the equivalent sized copper pipe. You might want to run a 3/4" pex line to the bathroom. They do make copper transitions to connect to valves, or depending on the type, you can use a compression one with the appropriate internal sleeve that prevents it from collapsing when you tighten the compression nut. The elimination of most of the elbows, etc., can reduce the friction, but you are starting with a smaller pipe in the first place if you go with 1/2".
I think that the crimp rings require more time to install; partly because you should use the go-no/go tool to verify each one. Plus, sometimes, getting the crimp tool in can be a problem. But, if that was the case, you probably would have a similar problem with the expander. Maybe not, though, since the expander goes in the end of the pipe while the crimp needs to go perpendicular to it. I've only seen it done, (and been the recipient of the results), not actually done it myself, so take these comments in that light.