The Swifty kit is very nice (especially the dual rad setup), except for it's use of 3/8" tubing. As for Asetek's kit, I've heard some good things about it, but I've never been impressed with their waterblocks, and I've had nothing but trouble with the Hydor pumps that they use. I'm not sure, but I think they also use 3/8" tubing. That's not saying these won't work well in your system, I just think there's a better way to go.
In my opinion, it really isn't that much more difficult to put together a DIY setup than it is to buy a kit. Think about it. If you buy a kit, you're still going to have to mount the waterblocks and the radiator, cut the tubing, clamp the connections, fill the system, bleed the air out of it, etcetera. For a DIY setup, the only extra work that you're really doing is getting all of the components in one place.
Admittedly, this isn't true for a completely self-contained kit like the Exos, but for the ones that you're looking at, you're buying a small bit of convenience for some extra money and inferior performance.
Just my two bits.