We see occasional confusion, in Blogger Help Forum: Get Help with an Issue, about installation and use of Followers.
The Blogger Help article is about using Following - once it's been installed.
This blog owner wants to use Blogger Followers - but is not finding the expected selection, in "Add a Gadget". The confusion is not hard to understand, given the relative visibility of Blogger Followers vs Google+ Followers.
The two gadgets are in separate sections of "Add a Gadget".
The "Google+ Followers" gadget is in the Basics list, while the "Followers" gadget is at the bottom of the "More Gadgets" list.
Look in the main, "By Blogger" list, for Google+ Followers.
Look near the bottom of "Basics'.
And there, we see "Google+ Followers".
"Highlight your total Google+ audience (both its size and some friendly faces), and offer visitors the chance to follow you on Google+."
Look in the secondary, by third party providers list, for Blogger Followers.
Look at the very bottom of "More Gadgets".
And there, we see "Followers".
"Displays a list of users who follow your blog."
Hopefully, with the Followers gadget being redesigned, this inequality will be reduced. Until it is, just understand how to find each gadget.