Can we say that hard drives that are already built as external drives have any special features?
Yes. Some external hard disks are housed in shock-resistant, drop proof/water proof cases, to reduce the likelihood of accidental damage.
https://www.amazon.com/LaCie-Rugged-External-Portable-LAC9000298/dp/B00IRV005E
Portable drives containing spinning disks are still more likely to suffer damage than portable SSDs with no mechanical moving parts inside.
I moved over several years ago from WD and Seagate 4TB 2.5" USB3 portable laptop drives to Crucial X6 SSDs (now available as faster X9 and X10). The prices of SSDs is coming down, but they may still be more expensive per GB than some spinning disks.
I have two questions:
1- Is this safe?
2- Why are hard drives that are already manufactured externally more expensive?
1). In my estimation, portable spinning disk drives are not as safe as portable SSDs when it comes to shock resistance. When a spinning hard disk is running, it's more susceptible to permanent damage (head crash) from bumps and knocks.
However, if an SSD dies completely on you, it's highly unlikely you'll get any data back. A recovery agency might be able to retrieve some/most/all your files from a dead spinning disk drive, if the platters are intact.
2). Sometimes you only get a 2-year warranty with a USB3 spinning hard disk, but a 3-year warranty with exactly the same model when bought as a separate item. In part, you're paying for a longer warranty. Also, a manufacturer can offload excess stock in USB enclosures, that aren't selling well as external drives.
When buying portable drives for "shucking" you can't be certain of the exact disk model number inside, until you interrogate the drive. You might get an Enterprise class drive (a real bargain) or a commercial drive with known life expectancy issues. You take pot luck with USB drives.
I've had good results with Inateck USB enclosures with SATA hard disks and SSDs.
https://inateck.com/collections/har...losure-with-usb-3-2-6gbps-transmission-fe2014
Inateck enclosures usually come with UASP.
https://www.minitool.com/lib/uasp.html
I've also tried a few AliExpress USB SATA enclosures for $3 or less. They are cheap and flimsy. No guarantee as to how long they'll work.
When travelling around over bumpy rough roads in Jeeps, I feel happier with portable SSDs in my luggage instead of HDDs, but I still make multiple copies of all files on at least 3 different drives. In addition, a couple of Crucial X6 SSDs are much lighter than a pair of 4TB Seagate HDDs.