The current price needs an update. People are willing to pay more than 6 keys for it. Somebody even offered 8 keys, but most offers are in the range 6-7 keys. Proof is below.

Sellers:

http://www.tf2outpost.com/trade/8148879 - 10 keys, unsold, 3 weeks, best offer - 8 keys

http://www.tf2outpost.com/trade/8590324 - 9 keys, unsold, 3 days, best offer - 6 keys

http://www.tf2outpost.com/trade/8611069 - 8 keys, unsold, 2 days, best offer - a strange festive fish (7 keys in items)

http://www.tf2outpost.com/trade/8537163 - sold for 7 keys

http://www.tf2outpost.com/trade/8296364 - a scatter + a lime fast learner sold for 9 keys (it's 6.5 - 7 for a scatter), also got offered 7 keys just for a scatter

http://www.tf2outpost.com/trade/8529025 - sold for 6 keys + 2 rec

http://www.tf2outpost.com/trade/8384206 - sold for 6 keys

Buyers:

http://tf2tp.com/trade.php?trade=9140899 - ~6.5 - 7 keys in items, 2 days, no takers

Quickbuyers:

http://www.tf2outpost.com/trade/8498304 - 5 keys + 1 ref, no takers

http://www.tf2outpost.com/trade/8246040 - 5 keys, no takers

http://www.tf2outpost.com/trade/8617975 - 5 keys, no takers

http://www.tf2outpost.com/trade/8250898 - 5 keys, no takers