Rare Kaj Franck Glass or Retro Rip off?  

That would be 'in the style...
That would be 'in the style of' and only loosely so--I'd guess they're of Japanese origin.
The Mushroom pattern, btw, isn't by Franck -- it's by Esteri Tomula. Franck designed the bowl (and other Arabia/Finel patterns) on which you commonly see it.
In particular, note the lack of detail in the mushrooms compared to the Tomula pattern.

Thank you for the extra info!
Thank you for the extra info!

I don't think it's 'retro'...
I don't think it's 'retro' but rather actual vintage just not Franck(or Tomula's). Glasbake used a similar design in some of their bowls and casseroles.