The only real reason to run a tubular manifold (header) on these is if you have say a T3 or T4 turbo flange setup, or whatnot. The heat retention on thick cast iron is far superior to most of the thin steel many of these 'shops' use, and equally important is the lack of inherent strength (think cracking) to adequately support the turbo, when using a header. Sure, you can add some reinforcement (I haven't seen any that do this right though), or if you did it from scratch - design it to incorporate, but overall...It can be done (say sch 80 pipe, coated, etc.)
Another reason I would want to run a tubular is to run a wastegate in the proper place (at collector, pre-turbo), but to do this right, you'd want a header that comes up high, so that you can have a long enough collector, although doing this has its disadvantages, as well. Equal length runners, properly sized would be nice, too, although runner design/size should be 'tuned' to what you want to accomplish.
We just don't have a lot of room, unfortunately, so you have to compromise. Sure, headers look neat and all, but there is a lot more to something that actually works well enough and IMO, 90-some odd % of the ones on the market are more for looks or bragging rights, so to speak.
With that said, just run an FP or even an EVO 3 ported and you'll be fine. I'd personally get them ceramic coated to keep the turbo running as efficently as possible (heat energy to spin the tubine), or make sure you at least run an oem heat shield (say with an evo). I personally ported and polished my FP, but out of the box they are pretty decent as far as casting manufacturing goes...
