As soon as you do this, all Fenrisian Wolves in your Space Wolves army get Initiative 5 and Leadership 7. It's certainly worth it for the points of one saga and makes Fenrisian Wolves a great choice if you have a handful of points left over, but don't know what to do with them.
Essentially a Space Wolf without any power armour, slightly higher initiative and slightly lower leadership and the ability to mov 6", fleet of foot and charge 12" -Fenrisian Wolves are an interesting Fast Attack choice in the Space Wolves army that can include 5-15 models and cost from 40 to 120 points.
Their only upgrade is a Cyberwolf to lead them and when you've already paid for an Independant Character to have Saga of the Wolfkin, a Cyberwolf really isn't worth the extra points.
Fenrisian Wolf Pack 1: 80 points
10 Fenrisian Wolves
If you think of Fenrisian Wolves like Kroot or Chaos Daemons in a Chaos Space Marines army, you can see the real value of them. Sadly, they cannot claim objectives, even when taken as Troops under Canis Wolfborn, but this doesn't mean that they can't contest them. Also, with their potential 24" attack range, they can suddenly bound across the battlefield and into close combat, unleashing 30 attacks.
With a healthy number of attacks and high initiative, they should tear apart light infantry with relative ease. Sure, you can take 5 Fenrisian Wolves, but you're giving away an easy kill point and if you take 15 of them, you're investing a lot of points in a relatively squishy unit which would be better spent on more power armoured Space Marines. I think that 10 Fenrisian Wolves is just the right size.
There are many Fast Attack choices in the Space Wolves army that will take priority over a unit of Fenrisian Wolves, but they're not a bad choice and like Thunderwolves, they will punish anyone from venturing more than half way across the board when they arrive from reserve.
But, they do tend to die due to their lack of an armour save. This means you either need to keep them in cover as a defensive unit designed to counter attack with their long charge range or only take on enemy units with low armour values.
Fenrisian Wolves are a really characterful unit that sets the Space Wolves apart from regular Space Marine chapters, so if you've got 80 points to spare and don't fancy taking a Land Speeder, why not give the Fenrisian Wolves a try and see how they fit into your battle plan.
They also a great accessory to give to Independent Characters when you're looking to bulk out a squad. If anyone's going to catch a lascannon round in the face, it's going to be an 8pt Fenrisian Wolf, not a 15pt Space Marine.
I'm going to convert mine from Chaos Hounds because they look suitably ferocious!