I've got both and yeah, they are worth $20. They are a good size and take a while to get through, though don't have a lot of re-read value. The first one goes into a lot of detail on all the main characters from the first two seasons. The second one does the season 3 characters as well as giving a little bio for every single bot that showed up in a crowd scene on Cybertron (Pipes, Huffer, Cosmos, Tracks etc etc). There are some funny one pagers too, like the send up of a womans magazine with Black Arachnia on the cover and various associated tips and interviews with other fembots. And of course there are episode guides, artist and writer interviews etc.
The Book Depository was out of the second book for a while and the IDW site was charging $50 for it!!! Def not worth that!