The transcripts were published day by day. There was some confusion when the inquiry went deep into the night, so each little volume doesn't always contain all the testimony for one day. On the other hand, some volumes contain as many as three days' testimony. I make it 15 volumes, the last one being only being the Digest of Testimony.
These little books were sent regularly to the Board of Trade in Britain. One went missing, which is why Day 2 is not on the PRO CD.
If the set is complete, a collector would probably pay a goodly sum. For practical use, I'd much rather use the searchable text created by Rob Ottmers and friends.