They combine tritium vials with fiber optics giving you the best of both worlds plus an aggressive slope on the front of the rear sight make belt racking a breeze.
They work really well at dawn and dusk when ambient light most closely match the output of the output of tritium vials. Here the fiberoptics gather and magnify the light and make target acquisition much easier.
During the day they are very easy to use as well and they retain the Walther POA/POI
I have them mounted on all my EDC weapons...Don't leave home without them.
I really should have qualified my post this morning. I also have tried almost all the popular night sights being marketed and ones choice should be guided by how the weapon is used.
If the weapon is going to be an EDC than I'd highly suggest the TFX Pros because of their robust design and construction. Since I've mounted them none have shifted their sight zero even with the abuse of daily carry, frequent range proficiency training sessions and weekly (or more often) cleaning plus exposure to mud, dirt, sand, salt water and the vagaries of my daily routine.
No night sight will be entirely perfect and suit all your needs but these come close. They aren't easy to mount (you do need a sight pusher) but they are worth the effort.