Can you use a handheld light with a shotgun?
Absolutely.
Can you use it effectively?
Yes, if you practice.
Will the Harries technique work?
Yep, if you practice.
Having used both a handheld light and a Surefire forend, would I even consider reaching for a shotgun and a handheld light if I had a weaponlight-equipped shotgun sitting there as an option?
No way in *
*.
I mean it. No way. Full stop. Do not pass go, do not collect $200. The end.
Finis. The weaponlight is that much better. I have yet to meet anyone who has done a low-light course (which, by definition, allows you time to prepare and has zero real stress) with both who does not think that the weaponlight is much, much better.
I'm glad I learned how to do the drill without the luxury of a weaponlight. It is a good skill to learn. But if you're planning far enough ahead to consider learning how to perform a particular technique, you should also be thinking about putting a light on the shotgun.
In general, I agree with the 'less is more' philosophy of tricking out a shotgun, but the one tacticool doodad that will
always be on my 'serious' shotgun is a light.
Mike