I have both a Glock & an XDM40. My friend also has a Glock .40. After thousands of rounds, we both shoot better with the XDM. From a rest or free handed, the XDM is the most accurate. It also will shoot plain cast bullets whereas the polygonal rifling of the Glock cannot... a considerable savings if you reload & shoot a lot.
Since I have both, I am not just giving a good review to the "one" I own.
The grip safety has not caused any problems. Quick draws, weak hand shooting & everything we threw at it, never caused it to malfunction or have an issue with the safety. Honestly, not sure why it is there as the trigger safety is essentially the same as the Glock & should be sufficient.
I did upgrade mine with the Powder River Precision trigger & it cut my groups in half.
It took a few hours to fit/install, but was worth the time & effort. It has now become one of my favorite pistols to shoot.
I'm looking at the new Comp 5.25" XDM40, which may become my new target gun & I may keep the 4.5" version for protection. If I was exclusively carrying it, I may have went with the 3.8", but I like the 17round capacity of my midsize.
If you are looking for protection, go with the .40. It has much more knockdown power over the 9mm & the recoil is not much more. My wife shoots it & it does not phase her.