It was years ago but I recall high CPU usage being an issue in particular.
In general it's just not as battle tested as ceph and I needed something more bulletproof.
However I will say this: I'm sure that issue with the CPU usage was fixed (I was watching the GitHub issue) and you might not need your distributed FS to be CERN ready for your lab; AND the UI and built-in backups Longhorn offers are great for beginners so I'd suggest giving it a try if you don't already know you want ceph or OpenEBS Mayastor for the performance and so on.
Curious to know what issues you ran into with Longhorn.