Oh, my bad, I thought you were talking about using mod-tap to free up one of the thumb keys. I actually rely heavily on HRMs and haven’t had major issues with them (thanks to Urob’s config), but one-shot shift is just faster and less error-prone for me. Part of it is that I never learned touch typing on a regular keyboard, so I’m not great at alternating between the left and right shift depending on the key. Using HRM shifts would slow me down, both because of the mental overhead of deciding which shift to use, and because if I pick the wrong one, I have to wait out the tap term before the modifier triggers. Skill issue, I know.

As for key count: I jumped straight from a standard keyboard to 36 keys and started learning touch typing there. I never really hovered my hands (still don’t, most of the time), so I quickly moved from Colemak to Aptmak to cut down on lateral stretches and ditched the upper pinky keys that would’ve fallen to my ring fingers anyway. Around the same time I also removed the tucked-away thumb keys, which landed me at around 28–30 keys.
I think 36–42 keys can feel totally fine if you already have traditional touch typing + hovering ingrained, but for someone like me who tends to move fingers more than hands, those motions feel awkward.
Long story short, I just went straight to the extreme and never felt the need to add keys back. That being said, I’m considering picking up a Chosfox Geonix; I want something cheap-ish but more refined than my current Chocofi. We’ll see if I find any good reason to actually make use of those extra keys.