I've never used a Laserlyte product, but I do have the Crimson Trace LG-405 for my 642. The 405 model is not any larger than the stock Uncle Mikes boot grips it replaced.



The LG-305 model by Crimson Trace is larger. It covers the entire backstrap and extends the grip length.



My biggest concern with the Laserlyte product would be the activation. You have to remember to flip a switch on the right side of the frame. If you are a right-handed shooter, that means you are going to have to shift your grip at some point to do so, whether you use your trigger finger or use your left hand. That's fine if you are at the range, but not so good if you need the weapon in self-defense. The grip activation of the Crimson Trace is what makes their product so excellent.