The Duratec product is interesting. I would think that getting it to look "neat" would be the biggest challenge. The fittings are not cheap, but it may equal out in the end. As to the argument that "black pipe cools better", I'd like to see someone prove that. I'm a mechanical engineer that has worked in the commercial refrigeration industry for over 20 years, and a good portion of that has been with refrigerant-to-air and fluid-to-air heat exchangers (evaporators and cooling coils.) There are 3 resistances to heat transfer in a system consisting of a higher temperature fluid inside a tube and free or forced air convection around that tube. There is the fluid to inner tube wall resistance, the resistance of the tube wall itself, and the resistance of the outer tube wall to the surroundings. The wall resistances are not dependent on material of the tube, only the tube wall resistance is. These resistances add just like electrical resistances in series to produce a total resistance to heat transfer. Typically, the wall resistances are so much greater than the tube wall resistance (maybe 10x on the inside, and as much as 100x on the outside in free convection) that large changes in the resistance of the tube wall has no appreciable affect on the system. Cut it in half, double it, change it by a factor of 10, and you won't be able to tell it in the real world. To top this off, you typically don't have that much delta T to drive heat transfer. The air coming out of your compressor tank is not that hot, unless it is running continuously on a hot summer day.
My system is copper, 3/4" mains and 1/2" drops, all Type M. In 2007 when I put it in, that allowed me to do the best piping practices with the least trouble, and was the most economical. I have a wall penetration from the compressor room to a main regulator and water separator ~54" off the floor, a vertical riser to the ceiling teeing into 2 mains of ~60' total length. There are strategically placed unions, and the mains are pitched properly. The drops come off the top of the mains, and U-bend back down the wall to a proper moisture trap. Everything is hung from short pieces of Uni-strut with Vibrasorb clamps.
This system probably has a total of ~150 solder joints in it. When I was done, I had one minor pinhole in one solder joint. Took all of one minute to fix. If I had attempted that system in iron pipe, I'm certain I'd still be chasing leaks 5 years later. As a matter of fact, you could say that I am. I do have a few pipe thread connections, and one of them, a 3/4" street ell to main shutoff ball valve out of the compressor, is one that I have never been able to get to entirely stop leaking. It has been apart 5 times, and sealed with PTFE tape, PTFE paste, combinations of the 2 together, and finally some industrial pipe dope that's mostly lead and is meant for high pressure gas piping. It still seeps, though a very small amount.
I have nothing against iron pipe as a material, but I sure do against the connection system. There are many superior connection systems out there.
