I would advise you not to give money to those type of developers. They are no good for the ecosystem. There's no legitimate developer who has 5 of the same app. They're just using cheaply bought templates, tweaking them, and publishing them to the store.
I'll give you an alternative way of doing it.
There's this site called IFTTT that lets you create "recipes" for different things. You use a "channel" that communicates to another "channel" to automatically do tasks. In this case, you'd want to set up a RSS channel to talk to your e-mail, or a $5 app called Pushover. Either way, you'd get notified whenever new freebies are posted via RSS instantly.
Here are some pre-made recipes for Kindle deals:
https://ifttt.com/recipes/search?ac=...age=3&q=kindle
Best of all, you can create them to work with various sources. So you could even get an update whenever any of the writers here at MR post their freebies too.
https://www.mobileread.com/forums/rss.php