At least one of them (the CK-12 calculus textbook available at

http://cafreetextbooks.ck12.org/math/CK12_Calculus.pdf ) uses bitmap graphics for all mathematics --- not even bothering to line things up on the baseline and using a mix of Computer Modern (in w/ text) and Times / Symbol (for labelling figures).

Absolutely wretched and along the lines of one of my worst experiences w/ a boss attempting to outsource composition work.

Sometimes ``free'' is too expensive.

William