No, it's a terrible idea. And, Dan's right, I've had Ron's experiences, and Christine gives good advice.
Here's why it's a terrible idea - it's lame. No other reputable agent will come in and give you a second opinion while your home is listed and on the market, so you're left with the other kind of agent.
This may not be the best idea, but I think it's a good one: tell your agent why you are unhappy with them. It's possible that they think you approve of their behavior, whatever it is. It's also possible that they don't care what you think - but you can't know that until you talk to them.
If you and them do not have that good feeling about each other, then ask for a release and tell them that you're going to seek other representation. THEN, and only then, should you go out and talk to other agents.
All the best,