I have the CTs on my 642. Its great in low light, or NO light.
BUT: The number one benifit I've gotting from the laser sight is it helped my shooting when I'm not using the laser.
The laser sight is the best thing to improve your shooting since dry fire. Meaning using the Laser sight while dry firing.
Dryfiring is great, one of the best things you can do to improve your shooting. Now add the laser sight to your dry firing.
When dry firing you cant really see what is happening on the target. With the laser, you can see the red dot jump around (or off) the target. You can make adjustments, corrections, to problems you didnt know you had untill you see that dot jumping off the target.
Laser sights are great, they help your shooting but the best part, they help your shooting when you arnt using the laser.
Dry firing with the laser allows you to correct your problems increasing your abilities when using the conventional sights.
Anyone considering getting the Laser sight should watch the FREE vedio on the Crimson Trace's web sight, and if all possible, barrow someones gun that has the laser sight and dry fire it.
You will be supprised.
The only ligit complaint I've heard on the CT Laser is 'WHAT IF THE BATTERY FAILS". If the battery fails you still have your conventional sights, you're no worse off the if you didnt have the laser.
Also my battery is over 4 years old and still works. If this bothers you, then get in the habit of changing your battery when you change the battery in you smoke detector.
Others complain of the cost, $200-250 per gun. So what, you'll save that in ammo, using the laser in dryfiring will help your shooting more then pouring $250 worth of ammo down the barrel which really dosnt show you what you are doing wrong.