I think the key here is having it optional. I am personally far more likely to sign up to something if there's google auth - I don't need another thing to track I can just easily assign it to my work or personal account.
Your location matters when deciding whom to entrust with daily business minutiae and the fact there's not a single bit of info there currently implies you have something to hide.
I will make sure the company details are on the website as soon as possible.
Overall, without conforming to the relevant legal framework, there is a risk of exposing both your operations and your clients, who may trust your invoicing software, to potential issues and non-compliance.
Consider making it possible to test the tool without signing up.
Is this for use in the US? Have you looked into electronic invoicing formats which are increasingly used/required in the EU ... I am curious if there is a similar move on the way in the US.
(As an example here is what the electronic invoicing format looks like in Denmark: https://www.oioubl.info/downloads/OIOUBL_Bekendtgørelse.pdf (scroll a bit past the Danish mumble to see the structure of the XML-documents interchanged.))
Im currently talking to users, and going country by country making sure its good.
An example, invoicing for Denmark works. Try it out yourself, its free.
I think its fine that they have to sign up tbh. Im not asking for any payment or anything before they try the tool and like it.
That is just my opinion though. If you find Zoho good, thats great as well.