if they fit your need, they work pretty well. I believe they're plastic though, so not quite as nice as fiberglass, but they do the job, and they're usually color matched to your car's interior.. so they blend nicely
they're terrible. I put some in a friends car. Don't get them unless you plan on using 5.25" speakers even though they say they may fit 6.5" speakers. They're also very flimsy and plastic. Its really the last thing you'd want to use to baffle a speaker. Also, I didn't like the imaging. They were more concerned with the best fit rather than the best sound.