Thought I'd try it out and clicked button top left of this page. The button changed to "Installed". I could then design a new form, or rather generate a sequential list of prompts a select whether response should be text, drop down selection for a number of other types of 'validation'. I wanted then to see how it works with Sheets. Leaving the page where I edited the form I could no longer seem to return to that page. I looked in my Installed Google Apps, in Extensions, inside Sheets and couldn't find anything even though the page 'chrome.google.com/webstore/detail/form-builder' says it is Installed.
At time I 'requested' the "App", I got a security warning in email. Fair enough, I'll revoke permissions and start again. No. The permissions are revoked, an operation that involved me changing password and on 3 devices, but apparently the "App" is still "installed". Where?
I can only give 2 stars because what I saw was OK, if simplistic, but it has cost me a significant amount of time wasted in trying both to use it effectively and in attempting, unsuccessfully, to remove it.
For the record I'm using Chrome on Windows 7 and somewhat peeved.