I've used them. Their control panel is not as pretty, and their community is not as large. But the product is arguably better, they offer things that DO doesn't offer like DYO ISO, daily backups for the same cost as DO's weekly (seriously DO, only weekly backups???), and a ton more.
I use DO and silently complain about the lack of daily backups. I don't really have a need for the other stuff, and Vultr is cheaper (when I last looked). But for some reason I always end up just using DO.