Good points. I would still encourage writing your own routine, if all you need is different timezones -- it would be trivial. I know that I have to work on many varying machines all over, and the more modules I have to worry about installing the more of a headache it becomes (especially when you're talking about hundreds of NT clients).
FWIW, I haven't noticed this package being "slow"... I'm merely pointing out that the author seems to think so.