I have one that I loaned out...does that give you any hints? I don't like them because you need to have teh room to shine the laser out at the reflective target, preferrably at 25 or 100 yards. If you're like m (and probably most other people) you probably mount your scope in your shop at home or even in your kitchen. Either way, you'll be lacking the space to put up the target at 25 or 100 yards, unless you have extremely understanding neighbours who'll let you staple it to their house and point a rifle at them.
I'd rather have the Bushnell bore sighter with the collets that go in the barrel. I've used them before and prefer them. Alternately I've also set the rifle up on a bench and pointed it out the door at the "O" on a STOP sign down the street by looking through the barrel. Then lined up scope with the middle of the "O" and gone to the range to test it out. Works pretty much as well as a boresighter, provided you live near an intersection.