Some are better than others, but none are worth the money. Since my 1st post I zeroed 2 rifles using the method I suggested above.
After manually bore sighting a 30-06 my 1st shot at 50 yards was 1.5" left. I moved the scope 6 clicks right and fired shot #2 at 100 yrds and was about 1' high. Since that is about where I wanted it anyway I just proceded to fire 2 more shots into a .312" group with no further sight adjustment.
Rifle #2 was a Ruger 10-22 that could not be manuslly bore sighted. I jus fired a shot. It was 8" left and 2" high. Before firing a 2nd shot I movd he sights 32 clicks right and 16 clicks down. Remember at 50 yards 1 click = 1/8". Shot #2 got me pretty close, but required 2-3 more clicks in both elevation and windage, but #3 was right on the money.
You can spend $20-$200 on tools to sight in your gun, some will get you closer to the bulls eye than others, but none of them will ever save you a single round of ammo when zeroing your rifle.