This addon is not even open source. Author can see all your email and contents in it. Look at his homepage and privacy policy. At least he is being honest about it.
It is upto you, users to trust this random man on the Internet with your gmail contents. I don't know why Mozilla has this under "Recommended" section.

First too get notified for all that website its okay with us

How do people trust their data to a random guy's extension instead of googles relatively solid service never ceases to amaze me.

"Checker Plus for Gmail" has gone from excellent to completely useless overnight! This extension worked well until a few weeks ago when the wheels came off:

I can no longer add gmail accounts! I have 3 accounts. There is a very weird "option" in the "Preferences" tab: "AUTO DETECT" or "ADD ACCOUNTS". I never had trouble with this in the past, but now if I select "AUTO DETECT" I cannot add an account, and if I select "ADD ACCOUNTS" I get an error message from "Checker Plus" when I try to add!

No idea what's causing this, but "Checker Plus" has now been relegated to the ranks of "NOT READY FOR PRIME TIME".

Best extension

I don't like to complain about a free tool but the border radius and information density of the new "modern" look are quite bad.

UI goes so ugly with the latest update

Themes

Genuinely this is a mandatory addon for me. I use it so often I actually paid for a free extension, dude earned it.

it works fine but i almost threw up when i saw the ui change please for the love of god stop making everything circular first youtube now this. let me change it back at least it's so ugly

The UI changed slightly in the last update and I don't see an option to roll back to the previous version. I have OCD and autism and this drives me insane.

Can no longer have more than 3 accounts attached to this without paying 20 dollars :(

By far the best Extension available for using Gmail! It works so seamlessly with your browser and auto updates and gives notification for new emails. It is highly customizable and works better than i could have ever expected! It makes checking your Gmail such an easy task, and even easier if you have multiple Gmail accounts. I highly recommend this Extension to any Gmail user!