I'm wondering if I use a metal thimble to 'catch' my needle on my bottom finger while I'm handquilting if it would dull my needle?

I wondered the same thing. I couldn't get the hang of using a thimble on the bottom, but I figured it would dull the needle quicker than my nice tender finger. I break a needle about every 10 hours or so, so maybe that would happen before it got too dull.

I would guess so. I've tried using a thimble on my bottom finger and even those little stick-on metal things and I just can't get the feel of it that way. The metal sticky thing was easier than the thimble though. But I rarely hand quilt and only a little at a time so my bottom finger doesn't get too sore.

I'm not a hand-quilter but I saw a video or a blog where the quilter used
3 different types of thimbles at the same time. As far as I remember she
used a leather thimble underneath. Maybe try that.

It seems like it would... sharp object poking into a metal object... that would have to dull it down. Right?

I can't use a thimble underneath. I tried it once but I couldn't feel the slight prick of the needle which caused my stitches to be longer than I liked. Sometimes I get such a callous on my finger that I have to use a different finger in order to feel the needle.