Pidgin and Adium are discussed in the guide specifically because they can do OTR. The trouble is that both clients are probably quite vulnerable to remote code execution bugs arising from things like memory corruption. Hence using them might protect you quite a bit from someone recording your IMs, but also expose you to someone who knows about a specific unpatched vulnerability and can send you messages taking over your computer.

The authors of the guide are very aware of this concern and will definitely be considering it further.