GoMailTracker serves its purpose. It's an MVP product, and that is ok. Again, for the price, you can't ask for a ton of features. I mean, we can ask for more features, since we are Sumolings and want the world at the cheapest possible price. :)

I would like more details about who opened the emails and which email address they used. It lumps it into a generic bucket.

Update: since I have been using the tool for about a week now, I am seeing more issues. The biggest one is that it just doesn't load consistently in Gmail. I am not paying attention to what plugins are loading, so I expect them to load. Only to find out an email I wanted to track didn't get tracked.