i bought the Osmo mobile to use with my iPhone 7+ and I have found that I am not doing so because of the shaky video issues.

Thinking about switching to the Osmo 4K instead.

What do you think?

I made the switch from OM to the Osmo+ and I don't regret the decision a bit.  My reasons are: a)  I don't need my phone in order to film something b) I can remotely control the camera c) it has zoom and most importantly the app stutters like crazy when recording 4k on my Nexus 6p so that problem goes away with a dedicated camera that records straight onto an SD card.  There are a couple of downsides to consider though.  You will no longer get tracking--as far as I know it's exclusive to the OM.  The sound is terrible so you'll have to make an extra investment in an external mic.  Hope this helps!