All night sights are tritium, and tritium has a half life of about 12 years. With that said, as long as the actual viles stay intact, they should all last about the same. Beware of prices that seem way below retail. When manufacturers have inventory more than a couple years old the sell it off to wholsale outlets and ebay stores where it is sold cheaper, but without warranty. I always buy sights directly from the manufacturer.
XS big dot sights
For the SK I would go with the Meprolites. They are the HK night sight option.