Slower than optimal is not automatically too slow. Yes, everyone should have a way to monitor coolant temp to the degree, even if only periodically (like hooking up a Datascan or ConZult every now and then). However enough people have been running UD pulleys for long enough, through track days, hot climates and extended idling, that there really isn't a case that the UD pulley without the OD pulley is a serious danger to your engine. If you're not having cooling issues and buy it just to have it then you're "fixing" a problem that really isn't there. I'm all for having a car properly sorted out but I'm not really into buying things I really don't need.
