Anyone have issues with the base or tactical model 509 mag release? I remember hearing in the past folks had a hard time depressing the mag release fully since it was ambi and the other side of their hand would stop the mag release from fully engaging.

Yes, I have this problem. Which is one reason why I would never buy a 509, even though I think it's a good gun overall.

Never had that problem, but switched to an Apex magazine release because it's more ergonomic.

I had that problem with an original 509 (non-tactical), so I bought a single-sided mag release from Midwest.  https://www.midwestgunworks.com/fn-509-magazine-releases.html

Completely solved my problem.

I have never had this problem but If you don't like the ambi mag release, just buy the apex single sided mag release and call it a day. If you are too cheap for that, take the factory mag release out, shave off the side you dont use with a dremel or belt sander.

I dont understand why people like to make mountains out of mole hills.

It’s not a problem with the mag release. It is a problem with the mags.

The mag is retained in the gun by a little nipple on the mag release. The nipple presses up against a ledge on the mag. Pressing the mag release left or right pushes the nipple off the ledge.

The problem is the ledge isn’t completely flat. So as you push one side of the mag release, it is actually pushing the mag higher up into the gun. To fix it you just file the ledge on the mag flat. Done this on multiple mags and it fixes the problem.

I also ended up getting rid of the ambi mag release. My grip pushed in the release on the right side, especially if activating the X300. Would occasionally drop mags unintentionally while shooting, especially with a fully loaded extendo. Would also push against my hand when purposefully trying to release a mag.
I just switched to the single side mag release from Midwest, fixed the problem.
I also installed an Apex trigger to make it perfect. Eventually ended up installing the HD striker, failure resistant extractor and spring kit for peace of mind even though I didn't have any issues in the first 2k rounds or so.

Zero issues with the mag release.

I have smaller, thinner hands though.

Midsize MRD is my EDC.