Chain stretches the most when new, so for the first 200 kilometers, you'll have to readjust the chain tension a couple of times.
After that, it settles down and you'll need to readjust every 400 kilometers.
It's no big deal. Takes less that 2 minutes.
My situation is a bit different as i'm towing heavy loads; putting significantly more strain through the shift kit and chains.
In my application, a base grade Shimano HG-53 9 speed chain lasts 1000 kilometers before breaking in half - an amazing distance considering it's small size and light weight.
Surprisingly, i breaks from fatigue, not wear.
Up until breakage, the chain is within stretch specifications of 0.5%.
Just incredible how well made and durable these chains have come to be.
The shift kit comes with protective covers for the jackshaft output sprocket so you can't get anything caught in the chain drive mechanism.
I don't use the protective covers, preferring the exposed gear and chain "look" - chains and gears spinning around are captivating to watch.
To prevent my jeans going anywhere they shouldn't, i use bicycle leg clips, stopping the leg end flopping about and getting caught in the system, if not using the supplied protective covers.
Photos of my bike and trailer setup in the links- best explains how much load and stress is going through the SickBikeParts shift kit and chains.
One word of advise - get the "Deluxe Shift Kit" as it comes with the rebuildable heavy duty crank bearing and tool assortment and some quality extras.
http://www.motoredbikes.com/showthread.php?t=23281
http://www.motoredbikes.com/showthread.php?t=23059
Cheers Fabian