I don't see why an externally-enclosed SSD will "last" any differently than an internal one.
i have multiple ST500LM0 drivss they are the seagate 500 gb + 8 gig ssd drives
they say they are 5 v .7 amps and usb 2 should be .5 and usb 3 should be .9
but they randomly disconnect, and they beep on me. its not the click of death its a weird beeping noise the drives make when it no longer spins.
its hard to find enclosures with external power supplies now
even though i have these drives using 2 usb ports ( for extra power ) plus i have it connected to a powered usb hub, they still stop spinning on me and disconnect and i get constant notifications on the mac that they ejected improperly.
i know that SSD drives are less then .3a @ 5v but i wanted to warn people about hybrid drives being connected to usb
one of the best features about the macs is they have special usb ports. and they can supply up to 5v @ 2100ma but first the device has to ask for the extra current. and the only thing that asks for the extra power supplied by apple are all iOS devices
i also have a seagate Momentus st9500423as in a externaly powered rocketfish enclosure. if it wasn't for the external power supply, the drive wouldn't even spin up
since 3 out of 4 hard drives are SSD hybrids, i think this post was semi relevant