I have two of them, both have the same pushdown tip/spout that unscrews for filling. The brass one that I bought works great, never had an issue with it.
The other one is made from a horn tip I carved like my F&I horn and dyed the same, it also works great but has a smaller capacity.
I keep whatever one I am going to use in my shirt pocket.
Gettin back to the original post, I use 4F.
I tried 3F a few times in my .40s pan and it seemed a bit slower between trigger pull and BOOM. I never tried it in my .50 as I use 2F and don't bring any 3F with me when I take her out.
The slight delay could just be my perception as I've lost a step or two over the last few years too.
Scout