Pretty sure flat tops work ok, as long as they will touch each other in the series connection. I have a pair of 18500 laptop pulls in this one and it works fine, they’re about as flat top as they come.
Not glued, the bezel is crazy tight but can be taken off with perseverance… I didn’t break out the strap wrenches but DID grab a silicone pad glove for taking things out of the oven for a better grip.
All in all, I really like this one! I modified it’s baby brother the M2X-UT, but this one I’ll leave alone… ask around, that’s really RARE for me to do!