Assuming this really is 26.5mm tall and no shorter, it will fit and work in the Kayfun 5.

I've used an authentic Lemo 2 glass (which is exactly 26.5mm tall) in Kayfun 5 SKU 9513500 as well as SXK Kayfun 5 and the tanks assemble properly with no performance or leaking issues.

Only issue is that you get very slightly less juice capacity, but you shouldn't even notice it.