Sounds like it.
Also, Volumes are persistent, so you may want to rm -rf /tmp-mounted-on-volumes on app reboots. /tmp is usually ram-disk, so I’d imagine that it is way faster than what you’d get with Volumes (which are on NVMes): Early look: PostgreSQL on Fly. We want your opinions. - #21 by kurt
Besides, you can extend Volumes, too (but not make them smaller). So, assign only as much space the app needs: Fly Volumes overview · Fly Docs
Volumes also come with their own problems (app instance is anchored to the host where the volume is created, and this has interesting implications like app VMs turning zombies).
Also, take snapshots (kept around only for 5 days!) if you need them (unlikely, judging by the name tmp) and keep your monitoring in order.