Choosing a laser sight isn't as simple as looking at the photo and the price - or even them and the brand name. Above all, you really have to be sure what you will be buying - especially to compare among different ones offered! Otherwise, you will be disappointed.
The basic questions are:
1) What will it take to install the sight on my rifle, airsoft, or shotgun?
2) What comes with the basic laser sight itself?
If you want to be a satisfied buyer, you must know the answers to both of these two questions before buying. Installing a laser sight on a rifle, shotgun, or airsoft generally goes easily and is inexpensive; installing one on a pistol is expensive, troublesome, or both - as either the sight must be built into a replacement for a basic part of the pistol or holstering the gun may be very troublesome or even likely impossible to find a holster fitting it.
Ideally, the laser sight package - like the one for sale now on Internet Gun Show for $30 - will have every item needed to install the sight and have it running: the curlycorded remote switch, mount, batteries, and hex wrench for sightin. The only thing it won't include is the Weaver or Picatinny rail it mounts to - something not included because so many rifles and shotguns already have them, whether from the factory or something you already added long ago. Batteries being included will save you an expensive trip to the camera store in the middle of installation!
Laser sights lacking a curlycorded remote switch are cumbersome for rifle, shotgun, and (long gun) airsoft use. Laser sights lacking an in-the-grip switch are cumbersome for pistol use.