According to Mongoose book, Agent programs "are effectively specialized combinations of Computer Expert and Intellect programs." In other words, while both are "intelligent", an Agent can only do computer stuff, while an Intellect program can make use of any Expert programs available to them.
To get an idea of why you would want to use an Agent instead of an Intellect, consider an Agent 1 could do Computer stuff with a skill of 1, occupying only 1 point of computer use. An Intellect trying to do the same thing would need 2 points of use--more hardware. Your TL13 transceiver (Computer/1) could run and use an Agent. It could theoretically run an Intellect... but there would be no hardware left for it to run any tasks.