We put a Drummer on Beth's XB12Scg 2 weeks ago. The standard one, NOT the econo. The sound is great, but she doesn't feel like there's an increase in power. We haven't had her TPS sensor reset yet though, so who knows.
We didn't want anything too loud. She also didn;t want anything she'd have to repack. She'd had a Vance & Hines on her Blast and it was annoyingly loud. The Drummer sounds more like a European twin than a Harley, I think it's perfect.
As far as which Drummer, Kevin says he may stop making the econo model... it makes less power down low and is "just for peopel who want something loud." We also considered the SpecialOPS muffler, but his dyno sheets also seemed to lack low end power, and he wasn't real good about returning emails.
By the way, Kevin's work is absolutely beautiful, and was easy to install.