Best Boresight for 12 Gauge

[squeegee]

I am putting a new scope on my Mossburg bolt action deer slugger. I really would rather spend the extra $50-$75 on a boresight, rather than ammo and save my shoulder the abuse. I see that there is 3 basic types?
1) laser 12 gauge shell that gets loaded
2) laser that screws in at the end of the barrel
3)regular magnetic one that goes on the end of a barrel

Can anybody recommend or discourage me from one?

Thanks in advance!
Squeegee

[Rebel Hog]

From your choices, #1