Fieldbook is obscure enough that it offers more privacy than Google Sheets (data directly linked to your Google profile, directly searchable by CIA/NSA, etc). Unfortunately Fieldbook is also Silicon Valley, ex-Googlers and ex-Grouponers so I wouldn't keep anything too private there. US privacy issues limit its usefulness.
The configurator allows total freedom in building your calculator, which comes with a slight learning curve. Once you've mastered it, you can build very sophisticated and powerful calculator forms. And even integrate quick checkout and payment.
Support is excellent, so you will always build what you have in mind.
And the product receives constant updates, so they're working hard on making the current experience smoother and adding additional features. I'm very excited about the product roadmap.
All in all very solid product that delivers on promise.