I have Trijicons that came from the factory on my Beretta 92G. They are adequate for daylight shooting...but they wouldn't be my first choice. I put a HiViz fiber optic sight on my P99, which I prefer for day time.
I'll echo what Rick said about the ease of installation. I was actually able to use a small socket to reinstall my front screw -- but a correct tool would have been easier. I used the Blue Loktite and it's solid 500 rounds later.
Night sights can generate a lot of debate. Some people won't leave home without them. Others (like me) question the likelihood that I'm going to be shooting at a target in the dark where the real value of night sights comes in. If there's even weak background lighting, I've found that the night sights get washed out pretty quickly. (But I have to say that in total darkness, they are VERY bright.) Rick already raised the issue of muzzle flash...your ability to see the sight in the dark will probably be gone after the first shot. It comes down to your personal philosophy on how you envision any engagements taking place. If you can, I'd recommend getting with someone who has night sights installed and trying them out to see how you like them. If you're going to use the pistol a lot for day time shooting (target, competition) then you'll probably want to be sure you're happy with it for that 99.9% of the time it gets used.
Just my $0.02....
Jim