I rated this as a 3 based on its usefulness. It works as it should and as promised, and it is a nice badge, but it doesn't seem necessary. You can simply add an image to you sidebar and link it to your Instagram for the same effect.
What this plugin needs is the ability to pull in user photos and place the badge beneath it. I currently use Instapress to pull in user photos, but that plugin lacks a badge link.
If you could combine Instapress with this plugin, it would be perfect.