Beware, this jumbled lot of songs is hardly "absolutely essential Roy Orbison". Out of 51 songs there are some 12 hits. The rest are a mixed bag of SUN recordings, a few sides from his short spell at RCA and a number of album fillers from his MONUMENT years, but without any form of continuity, mind you. Roy sounds completely different on the SUN tracks than on his MONUMENT ones. It makes sense to delve into the SUN recordings to get a picture of how he was working then, and it's a good idea to stop and take a listen to the MONUMENT album tracks that were recorded alongside the famous hits. But to mix it all in a bag does nothing for that kind of focused listening.
Elsewhere on Amazon there are excellent compilations of Roy's SUN recordings available, as are all the original MONUMENT albums, and I recommend you settle for them. A few years ago expanded versions of Roy's original MONUMENT albums were released, coupling the original tracks with contemporary A- and B-sides from singles. These are really value for money.
Or you may still want a survey collection, in which case you should check out the pricey but impressive 7-cd Orbison 1955-1965 box complete with a wonderful hardback book with a host of rare photos, logs of all the recordings and excellent liner notes. For a career-spanning overview, the 4-cd The Soul of Rock and Roll which covers Roy's initial success as well as his comeback in the 80s and the years at MGM in between. You can always argue with song selections in this kind of box set, but I think this is a lucky one. This also has a very nice book.