"it's kind of a worthless system if you can't change gears when hitting a decent hill with 165 lbs of trailer hanging off the back, and not much use even without a trailer."
I doubt that it could be modified to run with the shifter kits, The Gebe system is set up so that the toothed gears and drive ring provide the correct ratios for the engines torque. you can however adopt the gebe according to your terrain. The #11 & #12 gear are for climbing, the #13 & 14 gear are for speed... so yes you can climb a hill or pull a trailer with your kids or supplies.
http://www.motoredbikes.com/showthread.php?t=27227&page=10
This system has less parts to mess with, less things to go wrong, and although it doesnt use the bikes gears, most of the gears provided will provide plenty of power for the style of riding needed.
The thread is about how reliable this system is and the ability to change your gear on the go is also a benefit. Most peoples riding, will be done over the same roads day in day out, so you will be able to find the correct gear for your style. However lets say you want to go road trip, by bringing the extra gears you can change them out in a matter of minutes.
So yes it costs alot up front up to 3 times the price of a china doll but once fitted unlike a china doll the kit will probably last as long as you are able to ride the bike, with just a little tlc.
Of all the kits i own staton, De, gebe, electric etc, the Gebe is probably the most realible behind my staton friction drive, so i would not call it worthless thats for sure. Like i say don't knock it until you have tried it.........