Relying on a tool that offers no SLA is sketchy, especially if it’s going to offer an important component. If Jira goes down, not a big deal. But if part of my application breaks because of a third party tool I’m paying for to be up and functional, I’m gonna be mad.
It might be far less than ideal, but I was under the impression that's pretty standard. Unless you pay for an enterprise plan (and possibly extra on top of that depending on your SLA requirements) at best you'll get a billing credit for the downtime.