Hi Octo,

FWIW, I typically jump from MoI to OnShape a few times during the production of a model. It's typically about a 5 minute round trip:

1. Export to STEP making sure dimensions are SET to working model size (I typically choose mm - it's in the PREFS)
2. Import STEP into OnShape
3. Apply FILLET
4. Export STEP
5. Import back into MoI

It may sound like a lot, but the overall workflows and ease-of-use while working in MoI offset the occasional roundtrip to OnShape. Furthermore, there have been times when OnShape wouldn't fillet either, which points to a flaw in my model-- which I can typically fix in MoI. HTH