The $600 is a bit high. According to one of the links, the Retail on that cue was $1,000 which means it sold new for maybe $700-$800. Check ebay if you want to try to find anyone else that sold one of them, or do a search in the For Sale part of AZB.
I think 600 is alright for the cue, if it truly is in mint condition as you say.
As for the value changing, being a production cue, it's only going to go down the more it gets used. Numbering doesn't really do much for cues as it does for other collectibles.
If you're looking for a solid playing cue, it's an okay deal.
If you're looking for an investment that may increase in value over time, look elsewhere.