Depending on what you are shooting through, the chance of the following rounds being put through the hole made by the FMJ are slim to none. Sure, if you are shooting through plate glass, it might work, but most everything else will go into it's own hole. I cannot shoot one hole groups on a range with no stress, so there is no way I'd ever expect to do that in an actual shooting situation.
I think he meant that the criminal would be hiding behind something and the first two FMJ would take care of the problem. Glasers would be in case of a shoot-out. Not sure what would happen if the criminal was just standing in the open?
If the FMJ is enough for the job then load them up. Don't recommend that but
If you are worried about over penetration then use the glasers. Again personally
Why not just load up with quality bonded hollow points or an equivalent loading. Amazing thing this concept of modern defense ammo.