My current employer uses Jira, and I find it to be decent. I've used Asana in the past, and I like it a lot, but it has its own holes and pain points. Same for Pivotal Tracker, Github issues, Redmine, Bugzilla... Every tool I've used has had some strong suits and some drawbacks—mainly related to how well it fits with the project and workflow. A big plus is if the tool has a good API (REST, plugin, etc.) so that I can easily write tooling to reduce friction.
Unless you can find a really strong selling point—and I don't think offline support would qualify, for most people—I don't see it getting much traction.