I have never been a fan of cables routed under the bottom bracket. When clean and nicely lubricated they work OK but performance soon degrades, particularly in mucky conditions and gear cables have a tendency to stick, always at the worse moment when you are tired at the end of a long ride.
I have had my Corratec Bow for 6 months now and love everything about it, except for the sometimes clunky rear gear shifting.
I had already swapped to an XTR gear cable (Teflon coated) which improved things slightly but when it was time for a new block and a general service I decided I would try a new direct continuous cable approach.
Using a tip picked up from MBR magazine a few years ago I used some rubber O rings and a zip ties to make cable mounting points and routed the cable in a nice curve all the way down the bikes signature continuous chain stays to the top pull rear mech.
The difference is amazing making the bike perfect, slick shifting gears at last.
Holly has been struggling a little with the strength needed to turn the SRAM grip shift on her Isla Bike. I noticed this too had a cable route under the bottom bracket so thought I would change this to a continuous cable and see if it made shifting any easier for little hands. If it is better I will have a dig about in my spares and see if I can find an old XTR cable too.
I have also finally ditched a set of sintered front brake pads that with 
however much cleaning and adjustment I tried still howled and screeched under heavy braking. The nail in the coffin came when I nearly scared some horses coming down a steep road near my house. The riders were very understanding but I knew I had to do something.
So the bike is now working perfectly ready for its trip to Poland in two weeks time and hopefully Holly will be able to get to her gears more easily at her Lichfield City Cycle Club junior session on Monday night.