I have a Nightforce NXS 5.5x22x56mm on my .50, been there for 17 years now. It is one of the best scopes on the market and few measure up. I have had zero issues with it, even after it took a hit when my .50 partially fell off the bench.
Sure they're expensive but so are other quality scopes, they also have some of the best glass a scope can have. Warranty and customer service are second to none, so no worries there. Mine was $1,800 when I bought it, I think it's about the same price new if you buy one. The A.T.A.C.R. and BEAST are newer and have more/different features, ED glass... that's why they cost more.
I'll be in the same boat as you, doing a kit .50 and it will need a new scope or it will get the old NXS and the other .50 will get a new NF.