If you go for one of these kits T&T, and there's no real reason you shouldn't, make sure that you get either 4100k or 6000k bulbs.
As well as glare, colour is becoming a problem on a lot of after-market conversions, especially those fitted to boy-racer cars! You must have seen some very blue, solid colour headlamps on old Saxo's and the like. Don't confuse this with the shimmering blue effect of a genuine xenon headlamp, which by its very nature, has a thin band of verydeep blue, as well as the bright white main part of the beam.
Because the light isn't going through a projector unit, but is being reflected by the original shell, you'll never get this deliniation effect, all the light will be of a single colour and if you get 8000k or 10000k bulbs, they'll certainly have a blue colour and make you stand out like a sore thumb.
4100k is the standard colour temperature of factory fit xenons, 6000k gives a much crisper, whiter light and is the one I chose when I had one of these kits. In fact, it's the same colour I have now in my pukka headlamps.
Cheers,
Mike