I have had very good luck with TAs, but there are horror stories here about TAs who never get back to you, fail to get you price reductions, and in general act as a major block to getting anything done. This applies to both internet TAs, who are sometimes just order takers who forget about you once they get the booking, and small local TAs, who may be overwhelmed or completely lacking in knowledge of the issues you care about. OTOH when you find a good TA it's great to have somebody in your corner in case things go upside down.