I've experimented this and really liked it. Works really well on the 2011 platform. If there was a time loss, it wasn't noticeable for me. Just a tap on the mag release as my weak hand leaves the grip position on it's way to a fresh mag. I like that I maintain my grip and keeping my thumb on the thumb safety.
Although it does not work on the Glock platform. Fast tap on the mag release makes the mag stuck halfway out.
Same here. I use it only for the 2011 platform, I've tried installing an extended button like the one STI produces but it sort of gets in the way and I've had my mags drop on me accidentally. But for single stack or a glock I have no issues using my strong hand thumb to release the mag.