Was this ever resolved?

No. It has something to do with dependencies, but I've checked them all and there doesn't seem to be anything amiss

Hmmm. I'm trying to understand whether this plugin is a worthy purchase or not. What's your opinion?

I'm still waiting to hear about this issue, as is, it's not usable with this error.

It's a very detailed builder, with a lot of moving parts and functionality. One thing I don't like at all is that you can't move form rows up and down in the GUI (just a "move up/move down" toggle would be great). So if you screw up in building a big form, there's no way to stick new fields into a new row in the middle or beginning of the form (not that I can tell anyway). I would say for building smaller forms where you need something more way more advanced than the Concrete5 form, it would be great. I've used it on another site to get cool fields in the form that aren't available in Concrete5.

I would recommend it.

There is a fix provided by the Formidable team:

http://www.concrete5.org/marketplace/addons/formidable/support/arra...