You will not regret buying the DW621. If I were only able to own 1 router, it would be the DW621. While many here will suggest one of the multi base kits the DW621 is one of the best do it all routers, hand held.
I think the weakness of this router is in table use. Not that it won't work, but it will not work as easily as some other models.
If the router is in as good a condition as the add claims, it sounds like a good deal. Take a look at Pat Warner's router site for a review of the DW621
Keep the board posted on your decision.