The firewires work well strapless. Really nice flex. Probably the nicest flex for kiting I have felt. Like a lively version of the flex of a single four "s" top and bottom on crisp eskimo poly on the first day you ride it. Way better flex than surftech or any production kiteboard. But the durability is minimal. The old ones were fairly strong and could give a month or two of riding but the new ones have a different deck sandwich skin that is much weaker and dents and delaminates really fast. If you can get lots of them for free they are great. If you have to pay 800$ a board and it starts falling apart in ten sessions.........Well, that's up to you.
The key to firewires is the super light core, no center stringer, lightly bonded thin deck skin and balsa rail. (you never want to combine balsa rails with a center stringer as flex is hideous) It just can't take the abuse of kiting. They get flexed out as center delams and then just bog.
The best one is the 5'11" flexfire (old style) followed by 5'11" flexfire new style followed by 6'0" flexfire.
The new Taj model has a flat bottom "stringer" the makes boards harder to break but it doesn't have the soft flex of the others and it falls apart just as fast because the deck is the same.