Great how 1 person can build this. And even offer it for free. Love it even after a short play with it.
Is this better than Zeplin.io?
I am not sure, but I do know that Zeplin isn't free.
While they definitely do some similar things, comparing them is not straightforward. Zeplin is basically what Measure would be if you were to turn it into a hosted service. That makes Zeplin great for collaboration and sharing. Measure, on the other hand, is just a set of tools. You can export an HTML-based spec and do whatever you'd like with it (host it on your own server, put it up on dropbox, zip & email it, etc). I also find it more closely integrated into Sketch as an extension of its design tools. Conversely, using Zeplin takes you outside of Sketch to finish your annotating. I like having my annotations close at hand, embedded in my layers for full control— so I prefer Measure over Zeplin in that regard.
Both are great tools, just depends on your workflow style/preference.
Fantastic plugin, especially the "Spec export". This is a key part in our workflow between designers and developers.