Everything I buy is a referb (camera, lenses, etc). My theory is that since it went back to the factory due to something (any possibility) the factory has gone through it and checked out everything so you know it all works. Brand new and the item has probably only been partially tested if at all. Never had any issues and the money saved went to by another refurbished lens.
Go for it!
I've had issues with Adorama and B&H both selling me open box items for new prices (filters). I objected on both occasions and BOTH companies refunded part of the purchase price and were VERY NICE about the confusion. I suspect the mistakes made were due to human error not anything malice. As such I still shop at both companies.