Very strange. Normally he wants a flat(tish) field for astronomy, but he raves about these despite pronounced field curvature. And he sold off his 15x56 SLCs for these! How much better could they be? Oddly he doesn't do any sort of comparison.
I have both and the SLC is the grab and go glass for the night sky, I use it hand held in a reclining chair. An excellent glass with the requirement for higher mag during the day. The 18X70 has a very nice APOV and with the 18X provides really nice views at night (mounted), one can use it hand held, but the weight/girth after a while is uncomfortable, additionally I would never use in the day as it is IF. I would be the other way around, the SLC stays, the Nikon is a pure astro glass IMO, personally I have no other use for it.