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I don't think it's just the fan. The difference is the "premium" versus "standard" model.
The premium has the fan, as you say, but it also has the crayford focuser - which is a HUGE step up from the standard rack n pinion that you get with the standard model. It's worth it for that alone.
Having said that, you can buy the 10:1 crayford focuser which is even better again (in some cases - QA issues?) for around $120 and fit it yourself.
The fan is good though as well - it helps to cool the mirror to ambient temperature quicker than if you don't use a fan.
There's a bunch of threads about the crayford focusers in the Equipment forum - do a search and read what people have to say about it before making your decision.
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