Thats not a bad price, a Synology 4 bay NAS is around $600. CPU DOES matter if you start to team and setup drive caching. This thing would beat the pants off a regular small business NAS. Before you buy I would check for drive size limitations, can you stick in 4TB drives etc. What is the RAID card, limitations? Personally two NICs for teaming will be a perk as well. The reason this is so cheap is this server in a data center is worthless. 2U server hardware this old is cheaper to dump and use half the space for more power and less rack rent costs.
Shipping would also be a concern as well.
If there is any drive size limitations just walk away dont even look at buying.