No, the "Nirvana Discografia Mega Exclusive" collection is not an official release from Nirvana or their record label, Universal Music. It's a fan-curated or third-party compilation, which may not have been authorized or endorsed by the band or their estate.
The sound quality of the collection may vary depending on the source material and mastering. Some editions might feature high-quality audio, while others might be lower fidelity.
The "Nirvana Discografia Mega Exclusive" is a compilation of Nirvana's music, released as a mega-pack or box set. This collection is not an official release from Nirvana or their record label, but rather a fan-curated or third-party compilation.