Ive had two, a SIG specific, and currently, a Glock specific, and both have worked great.
The SIG tool did both front and rear, the Glock, just the rear.
With the SIG, using the zero "witness marks", I only ever had to fiddle with one gun after initially installing the sights. All the others were dead on when I got to the range.
The tool also makes sight adjustments at the range very easy, and with a lot more precision than beating on them with a hammer and punch. You also have less worry with the night sights and possibly busting a vial.
I pretty much paid for both tools by selling the old night sights I was replacing with new ones. Sold them on EBay for about half what a new set go for.