They work OK, but the Nytro's unique chassis required a ski with some good control and darting is deadly on this sled. I really liked the Simmons Gen 3 and even the Gen 2 on this sled. I also think the SLP Mohawk would be a good ski. SlyDog 8" Powderhound works well as well.
I was looking at the Powder Pros at the snow show one year and the SLP guy told me he would sell me some but don't be disappointed when there isn't much difference from stock.
I sell a lot of 8" powder hounds to guys with Nytros. They are like power steering and the extra width just aids even more with the floatation. I have a set on one of my sleds and love them.
Also, SLP now has the Mohawks that are slightly wider and less aggressive than the powder pros.