If you are comfortable setting up your own templates it does a great job sending and handling unsubscribes/statistics. It isn't simply hooked into the SES SMTP , it fully utilizes the AWS API. Sendy iteself has a simple api to add users to lists and do other common things. I've used it for years.
There have been a couple of bugs that caused me to have to dig into the source code - which as others have stated, is a mess. Though I suspect its been purposely obfuscated to prevent pirating.
If you ever wonder what's going on in functions.php, I've unwound it a bit - you can see its making a phone home:
https://gist.github.com/anonymous/cb21dfc35e1d4b74e136ebc694...
Shameless plug: I run https://mailblast.io, a hosted email marketing solution powered by Amazon SES.
>jmhobbs: The Sendy codebase is horrifying.
We use Sendy at work, 40k+ sends weekly. It saves us boat loads of money since moving from Mailchimp.
We've forked it, patched it, and use it internally, but only because it's cheaper than writing our own, for now.
I'm not telling you not to buy it, I'm telling you that the guts are shitty and you should know that before you fork over cash