Received a replacement SFL pair this morning, these have a much easier focus turn. After a quick comparison the 42NLs there's not much new to report. The NLs have a somewhat more comfortable and immersive view. I believe some would say they have a bigger "eye box." Not as widely noted is that they have a touch higher than spec'd magnification, reportedly measured at 8.2x. It is noticeable if you look for it. The NLs are known for their flat field, IMO the SFL view is flat enough and sometimes I appreciate a bit of 3D effect. Note that I use eye glasses and on both pairs of bins use 3/32" thick o-rings on the eyecups to help prevent blackouts.
As mentioned elsewhere, the SFLs have certain attributes that are generally considered to be in their advantage, such as price, weight, size, faster focus, greater contrast, lack of the cursed FP system and non-tearing objective covers. In my non-expert examination the SFLs resolution is virtually equal to the NLs, with both being the best I have owned.