I've used them several times to good effect, and really like them. I've never had any problem with strings popping out, and I don't use string trees. The only downside is the cost, but really, it's a one-time thing since the nut doesn't wear so I don't know why I complain.
Like any "trick" nut, the sound is only affected when you're playing open strings or chords, and then it's so minimal that if you're not listening for it, you won't hear it. But, there is a very slight brightening as a result of the string being against a metal termination vs. some sort of plastic/bone. Of course, as soon as you fret a string anywhere along the neck, you're terminating on metal anyway so no tonal surprises. In effect, the LSR ends up acting like a "0 fret".
Speaking of a 0 fret, at the very beginning of that video he takes Fender to task for their longitudinal placement dimension and offers up a corrected number. Problem is, he's measuring to the wrong point, and Fender is actually correct. The original nut is cut in such a way that the leading (body side) edge of the nut is where the speaking length of the string begins, but if you look at an LSR nut, the bearings the string rests on are back a little bit from that edge, so the speaking length of the string does not start at the leading edge of the nut. So, if you follow his instructions, you're going to have too much distance between the nut and the first fret, which is going to make a mess out of your cowboy chords. Not a huge amount, but it would be measurable and audible if you've got a critical ear.
His criticism of Fender's mounting depth dimension is understandable, and I'm not sure why Fender gives a number at all as that depth is going to vary from one instrument to another depending on how aggressively the fretboard was surfaced prior to fret installation and what size frets are installed. That's why they give you shims.
