It's bits and pieces but very enjoyable.
It's described on the cover as "A collection of previoulsy unreleased recordings, rehearsals, demos and alternate takes from the personal archive of the brilliant French jazz innovator."
Another other album of his, again released by Jazzman Records, is a "best of" compilation, which again is well worth getting:
http://www.jazzmanrecords.co.uk/the-best-of-jef-gilson-cd