This started as a personal project to watch some Twitter names that have been registered and never used. One account, I was following manually ended up actually expiring or was deleted. I wasn't quick enough to notice and register it.
Currently the plan offers 5 accounts for you to follow. If you should need more, you can alwasy get in touch with, by logging into your account and clicking your profile icon. In the dropdown there is an option to "email us".
When you start tracking an account, our servers query the Twitter API at various intervals throughout the day to check on the status of the account. As soon as the account doesn't appear to be in normal standing, we send an email to you right away.
Twitters Inactive account policy, states: Accounts may be permanently removed due to prolonged inactivity. The threshold seems to be around 6 months before a potential expiration can occur.
When you log into your account, there is a dropdown on the right side when you click your profile icon. In that dropdown there is an "email us" link.
Right now we have only one plan (5 accounts for $1.99 USD). We may expand those plans if there is further interest in this project.