I bought 17.5" silver Kaikias (the '08 model I believe) for my own Christmas present, and have no regrets. It has much better equipment than I could find anywhere else for this price. It comes in a box with most of the bits in nearly the right place... in other words you do need to know how to set up a bike properly to build this. But that's part of the fun, surely. If you don't want to be adjusting gears and bleeding brakes then I'm sure you could take it to your local bike shop. Nearly everything can be done with the allan key that comes with the bike.
Now I had a slight issue with mine, that the chainline was slightly too far out to get perfect adjustment on the gears at the front... it would have worked, and I'm kind of picky, so I wanted it just right. I got in touch with 2X2 who manufacture these things, and they were very helpful - I'm quite happy to recommend them as a company. I also had a brake pad fail, and made a warranty claim for that, which is fine (and that was a genuine shimano pad, so no fault of 2X2. Very unusual fault, so I doubt that will happen to most people.)
I have ridden the bike on various red graded MTB trails in Wales, in rain, snow, hail, thunder and all kinds of mud... and occasionally in sunshine... and have not exceeded its capabilities (although I have exceeded mine!) OK, it's not a specialist downhill bike - it's an allrounder. Seems sturdy enough to me. I even crashed it by jumping badly, and haven't managed to damage the bike. (Even landing on the front wheel and going straight over the bars... always wear a helmet! The bike was fine though.)
I would say if you want to thrash the black graded routes, then get a downhill bike with more suspension. Anything else this will do nicely. It goes, it stops, it turns quickly and is generally no trouble. Enjoy yourselves.