I just read the review of the Stallion on straplesskitesurfing and it prompted me to leave a true independent review here.
I own the Vanguard 5'2, Vader 5'1, and recently acquired the Stallion 5'2. I am 6'2 and 79kg.
I am not sponsored by any of these brands (I was a Firewire ambassador for about a year 4-5 years ago before the programme was shut down in Europe).
I have used these boards in various conditions, from 10 knots cross shore wind and 2m waves to 25-30 knots and big chop. I have about 10 sessions with the Stallion, 20 sessions with the Vader, and countless sessions with the Vanguard.
The Vanguard works slightly better than the Vader and the Stallion in lighter wind. It also has a better upwind ability. Not that the other two are bad at it - they're actually far better than your average kitesurf board in that regard.
The Vanguard is faster, but it his harder to make tight turns - the board wants to go straight and you have to put all your weight on your back foot to slow down and turn in bigger surf, which isn't ideal.
The Vader and Stallion are more closely related in terms of performances. The main difference between the two is the construction: the Stallion has more flex and that makes the board much more comfortable. It is also lighter which allows the board to stick to your feet when jumping; it makes all sorts of rotations easier to achieve. It has a decent amount of nose rocker which saved me from a few nose dives in the waves.
That being said, I find the Stallion prone to pressure dings, just like a regular PU surfboard. Mine is heavily marked when the Firewire don't have a scratch. Here's a photo of the hull side:
A friend told me his board has the same dings.
I don't have photos of the deck as it is covered with wax but there are large depressions between the PVC patches.
I also found the finish of the board very average, with deformed rails, see photos below.
It's a bit hard to make out as it is shot with my mobile but you can see that both the rail and the channel are curved. The tail has a negative rocker.
In short: I really enjoy the Stallion, and it is my board of choice for most conditions, but if you're looking for a long-lasting board, or a board that will keep some resale value after a year or so, I would probably go for the Vader.