Is the X5 adapter compatible with the Osmo+ handle? I'm on the fence on whether to get the osmo or the osmo+. The documentation says the X5 adapter would fit any osmo handle, but I have seen a few reviews say this isn't true. Anyone with first hand experience would be great.

I don't see why not, I think the osmo handle is universal, all the flavors of Osmo use the same handle.  Why are you getting the Osmo+ though if you are planning to mount the X5?

I haven't decided if I want to get the X5. I was just thinking if down the road I wanted to get it.