I would too in as much as I don't have one. I've always used a banger/puller anyway. I can see the issue (Lefty) with HC. It's inherently slippery.
BTW, I sent Len an e-mail and asked him about a sub forum for hand cast and factory HC lead pills and techniques for manufacture and loading.....
I would say (tongue-in-cheek) that if the Grip-n-Pull has smooth bores, it would not be a satisfactory puller for HC lead pills. You'd have the same issue as a collet puller, no grip on a soft (softer than gilding metal at least) outer shell.
Sectional density is much less on a HCL pill versus a normal hunting or for that matter, pistol round.
if the bores are serrated. it should work??
Maybe we will hear from the Grip-n-Pull folks???