Nair is a garbage move. After the first initial hit, none of the other hits do knockback or hitstun, the opponent can do anything to you while you are in this period of "You can't do crap while they can do anything" It's range is extremely crappy, it's punishability rating is through the roof. The only really "Good" aspect about this is that it has good priority (Due to Wolf's hurtbox being massively reduced) and little landing lag.
The ONLY situation I have found a good, non-punishable use for this is when I'm very close to the ground (Falling) , very close to my opponent, and my opponent isn't shielding. Then you need a quick hit move with little landing lag, it sends them away, and you go on with your game.
To me this simply has no other uses, in every situation it could possibly be used in, 99% of the time, there's a better, safer option for Wolf to use.