I have a Weaver rail mount NC Star, They are around $20 on Amazon. It is as accurate (as it's shooter) at 15 yards which is where I have the parabellum set because any use of it will likely be within that range. I have fired around 500 rounds with it under my FNS-9, I seldom use it, but to it's credit, it has survived that many shots without breaking or coming out of adjustment.
Personally, I find lasers useless (I could just about stop right there, a reflex sight is way more effective for target aquisitions than a laser IMO) in almost any kind of light. I can actually acquire a target quite a bit faster with my sights, even at really low light, I have awesome Trijion night sights, and would instinctively use them to aquire a target. Take it for a walk through your house at night with your tactical flashlight and see if you even like having a laser, if you ever use it, that's when it's going to come in handy. You'll still need the tactical light to help you through your OODA loop.
If I had to select between the night sights, the flashlight, or the laser, I'd pitch the laser first. I'm considering transplanting the laser over to my shotty and using it in addition to the attached flashlight, it is the implement of choice for midnight hospitality services.