We use it quite extensively and it's been great. The API is really well designed and hasn't limited us at all. Being able to send arbitrary event schemas is nic

We use it quite extensively and it's been great. The API is really well designed and hasn't limited us at all. Being able to send arbitrary event schemas is nice too. We were able to re-use an existing JSON document format with only minor changes which means we don't have to do a lot of mapping back and forth. I highly recommend them. (Disclosure: we partner with Keen IO on some product stuff, but we pay for our account for the analytics stuff just like anyone else.)