This is not a remaster. If you already own the original albums (Facelift, Dirt, Jar of Flies, Alice in Chains (Tripod), and Black Gives Way to Blue) in FLAC, you do not need this. It is a compilation.
If you purchase the physical "Essential Alice in Chains" CDs, you own the master. Ripping them to FLAC using software like Exact Audio Copy (EAC) or dBpoweramp gives you a bit-perfect copy. The CDs are Red Book standard (16/44.1), which is the baseline for "CD Quality" FLAC. This is superior to almost any stream. The Essential Alice in Chains 2 Disc Set -FLAC-
Standout MTV Unplugged versions of "Nutshell" and "Over Now". The FLAC Advantage This is not a remaster