I dont understand what you are offering, it seems like a more limited version of Google Analytics! Also theres mixpanel and tons of other analytics services. You need to explain your product a lot better and explain how you are different than all the other analytics platforms.
They are focusing on tracking and taking action for a special type of event (login). A retention email ("Hey, we haven't seen you for a while") is a great strategy to convert idle users into active customers.
Yes, anything that sends information in the URL is obviously visible to anyone who cares to look at it, and would breach most privacy legislation.
This is a good idea in principle but the execution isn't really viable in its current form. They need to re-think how they get the e-mail addresses and how they keep track of users.
In addition they offer no privacy policy. That means they have complete freedom to aggregate all of the information you send to them, via your app, and sell it.
This is a good idea, but I wonder about the shelf life. As more sites start to use email responses and follow ups it increases the chances that people start flagging this as spam or ignoring it altogether. Email is a valuable but delicate channel.
I wasn't sure what you were offering, so I clicked on "How it Works" where I learned how to signup by entering an email and password. Thanks for this useful information, I'm not sure how I managed up until now without knowing how to signup to websites :-)
Joke apart, I do think that it's a good idea but you really need to make it clearer. The first page is very vague: A dashboard that allows you to see what's going on in your operation? Are there any other types of dashboards?
You need to explain right from the beginning that you're product will help with sending emails to increase retention.
Perhaps consider working with a marketer?