It does look a whole lot smaller than an Epi-Pen in its plastic case. But Auvi-Q (existing epipen alternative) is also much smaller. I don't see any pictures of the neffy case; surely you have to carry it in a case just like the others.

Edit: Found a picture of an official case. Carries two doses and looks roughly similar in size to two Auvi-Q doses: https://andersresearch.substack.com/p/aquestive-therapeutics...

I bet a third party could make a smaller case than that, though. I also expect that neffy is much lighter, as Auvi-Q has a battery and a speaker and a needle and a spring and whatnot.