I will second the recommendation for the Vortex SPARC and here's why:
1) For the original poster's price point, he would be getting a new unit instead of used.
Yes the used optic is an Aimpoint, which will of course be argued as superior to a Vortex, but for the user's primary needs, an Aimpoint is probably overkill. Aimpoints have a high price point in large part because they are rock solid workhorses. They can take whatever beating you hand out and then embarrass you by asking for more. While that is awesome, unless you are a HSLD operator, it is probably more rugged than you need it to be for your range trip/home defense/even 3 gun competition. There is no point in paying for a feature that you would likely never fully utilize. In the case of the used optic, the primary user utilized that feature which is why the optic now has a value comparable to less "bomb-proof" products.
We see this a lot here at Optics Planet with EoTech as well. Customers want to know why an "ordinary red dot" costs $500 or more. "It's not even a green reticle". They don't realize that part of what they are paying for is that durability/reliability through all conditions/drops/situations (which most of your average recreational shooters will never fully require since we tend to "baby" our optics instead of rolling down mountainsides with them).
2) The SPARC is an excellent unit (my first vortex product and it has been mounted at some point on most of my firearms). Verry rugged, crisp, multi purpose optic that comes with a amazingly complete package as stated.
3) Vortex has phenomenal customer service
Sorry HR, didn't mean to swipe the question
-Matt S.