I don't have a Q8+, I have the original Q8 (2017) with the wide positive contact ring on the driver identical to the current offering with the Q8+ in the pictures in the review. I have run nothing but flat top cells through it without a hitch for 7 years, never had a cell imbalance issue.
The problem with button tops is the vast majority of lights perform best with unprotected cells which are almost always flat top only. Some battery suppliers will add a button top for you for a tiny surcharge or you could just add a round blob of solder to the center of the terminal yourself. But most readily available button top cells have an added length protection circuit which is more hindrance than help since it's only necessary with series battery applications (cell end to end) not parallel like the Q8+. The protection circuit adds unnecessary length and can cause fitment/damage issues. Unprotected button tops are rather like hens teeth, usually only Samsung and Vapcell offer ordinary production unprotected button tops.
You shouldn't be forced to pay anything more than $15/cell no matter what. Have you looked at cells on
www.sportlampa.com? Also NKON which I think is Netherlands based?
Main thing is you have flat top Sofirn brand 21700 cells en route in your lights. I think it's reasonable to assume they would never ship in that configuration knowing there was even a chance of improper cell contact.
I can't speak for Reddit but maybe they were using off brand cells of improper length or worn in (indented) flat top terminals.
I can say for certain that the industry standard is to utilize unprotected flat top cells for 21700 to maximize cross-platform compatibility.
The exception is the premium quality Acebeam model line, that have based every single model to fit the exact same proprietary (really LONG) protected button top with onboard USB charging 5000mAh 20A 21700 cell. I despise on board cell charging, only use an external slot (XTAR VC4+) charger. Many Acebeam models will accommodate a 4-5 mm shorter unprotected flat top cell but have less than perfect contact.
If you order an E75 It will have that exact cell.
For everything else the flat top Sofirns will be ideal.