I've used one in a Glock 19 as well as a Glock 43X/Glock 48 (both.)
Yes, it helps with recoil flip and muzzle rise, especially with multiple fast follow on shots (such as during a USPSA match trying to catch a couple quick Alphas on a close target).
As I recall, the difference in RSA weights between stock plastic Glock and the Tungsten RSA is not as much as they claim. I believe the delta was only 0.7 oz, comparing both. Now, this isn't a huge amount but it does make a difference. In particular, the felt recoil of the G43X was pretty snappy, and adding a tungsten guide rod helped me tame it a bit to be tolerable.
If there is a tungsten guide rod for the P365, I would guess that yes, you would feel the difference.
Seems like there was a previous post or two like this. I think you will find opinions on both sides. I like them and have them in my 226 competition guns, but haven't tried them in my 365 - don't need any extra weight.
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