Hi the challenger is a Gen 1 tubed nv, most of the ir out there are on a 850 wavelength , these work really good with digital nv and not with lower gen1 tubes.
I have a Challenger gen1 , haven't used it for a few years. But I will try a few of my ir units on it see which is the best, Also a lot depends on the scope you are putting behind.
the onboard ir is rubbish only good for a few yards if that.