A full install on a USB stick will make a perfect Fix stick. On a device with Persistence the Persistence is usually a compressed file which stores all of the data on the OS which is updated from the original install files. If the Persistence file should become corrupted then all data is lost. A main issue is that a Persistent drive does not allow for a kernel update. The full install will function just like a regular installation on a hard disk. The USB stick will make the OS more portable and, of course, allow for kernel updates.