IMHO, suitability depends on use case more than anything.
For portable, bus-powered use, which presumably implies writing data to drive, moving the drive somewhere else and reading back the data as a primary use case I favor SSDs because they are not shock sensitive, are lighter and typically much faster. If one chooses one with decent write and endurance characteristics for one's needs (decent size pSLC write cache, avoid HMB NVME drives in a USB enclosure, etc), I don't see an issue. DATA retention of an SSD during long periods of being unplugged is a consideration, however.
For long-term storage in a primarily read centered scenario, SMR drives might work well enough, but I don't really see the point personally as CMR drives are available in 3.5" form factors (externally power required) and I don't see a practical reason for using a bus-powered drive for this, personally.
If one actually wants to run software from or read/write large files from a bus-powered device, the only options that makes sense to me are NVME drives with a DRAM buffer or possibly SATA ones (also with a DRAM buffer) in a USB enclosure. Using a Thunderbolt with an NVME driver might be an option too (I suspect HMB works over Thunderbolt, but I could be wrong).
In all cases if the DATA is irreplaceable or at least not expendable, one should always have multiple copies of it (backups) and keep those up-to-date/synched.
Getting back to your initial inquiry, the first thing to ask is how you expect to use your drives.