We have recently started using Keen IO. We picked it because it's super flexible, and eventually we will want to expose some analytics to our users, which Keen is great at. But for the most part, in our super-early prototype, we specifically didn’t put in many analytics because we didn’t want to pay attention to them. At such low numbers, you want qualitative feedback instead. I'm tempted to develop a custom tool because any time I use an out-of-the-box tool, I end up hacking it and doing my own version of it anyway.
It’s very simple, casual and cheaper than MailChimp. I like it, but I probably wouldn’t pay for it. It’s essentially one step up from bcc’ing people on Gmail--a slightly more public version of what you’d send to friends and family for updates. At this point, the main things I was looking for were a sign-up form and the ability for people to unsubscribe. I didn’t want to pay for anything, didn’t need segmentation, templates, A/B testing, etc. We just need to notify people of updates and keep them engaged. We'll probably end up moving to MailChimp at some point.
QuickBooks Online is great, and super cheap. That said, it’s not intuitive, and it would have been really confusing without the help of our outsourced accountant. There’s really no clear documentation on how it should work. You really need accounting experience to use it effectively.