I don't have a leufken water kit myself... but I have been looking at them, among other kits. Leufken offers a great package - good reservoire, very large and effective radiator, and a well designed waterblock. The Aquastealth kit from becooling looks to be right on par with Leufken's, and both are about the same cost. As far as any obvious design flaws, Leufken doesn't have any... the retention clip is also very generous, and can accomodate spacers and peltiers later on if you feel the need.
If you want to go watercooling, leufken's kit looks like a great buy and should get you nearly identical cooling performance without a peltier as most setups would. When you do go watercooling, make sure the radiator is large enough to handle all the components being cooled, especially if a peltier is involved (leufken's is larger than some compact car oil coolers), and make sure your waterblock is well designed. I'll look around for some review links, as there are several excellent makers of waterblocks such as Tidal Pool and Dangerden, should you feel Leufken's design is inadequate.