hi andrew
IMO kz are a better bulb we sell both the ati and kz (in fact the only two we carry) bulbs while ati are def cheaper we get better reviews for kz and most people find they last longer then ati bulbs do.
just a FYI i gave you the kz at the ATI price since we were out of the ATI you wanted
let me know what you think of them and my offer still stands if you would like to change them out
cheers
denny
concept aquariums