DLP link 3D glasses

There are many DLP link 3D glasses on ebay, price ranges from $20 to $60+ each. Just wondering if there is any functional difference between them. What are the things I should look for when I shop for DLP link 3D glasses? If they are all the same, I guess I can take the cheapest offer, right ? The one below is <$20 each. Is it good enough ?

http://www.ebay.com/itm/2x-New-SainS...ht_5778wt_1006