I had the opportunity to listen to all 6 volumes from beginning to end. And while they all show Zappa in different bands and performing various versions of some of his  most difficult pieces, I would say that on the average, about 25% at most of each release would be considered "good". And by GOOD I mean a great song, with or without a great guitar solo or instrumentals that would blow you away. Personally, his "Flo and Eddie" period, is his worst. The off-key castrato singing of the thoroughly unfunny fat duo is - again, in my humble opinion - an abomination and frankly, a drag on the whole show. Zappa's various bands are the cream of the top performers of their time, and this pair of clowns do nothing for the music.