I don't have a RecTec or a downdraft. I know that when I talked to the guys at Blaz'n Grills, they had nothing good to say about downdrafts.
At this point, if downdrafts were worth it, you'd think every pit maker would have them either already installed or an option to buy from them.
The fact that none of the high end makers have them (or any of the low end right?) makes me think they're not worth the metal they're made from.