Hi rusty. I appreciate you're in "The States" so supply and availability, to say nothing of local preference and legal restrictions, will no doubt be somewhat different to us hear in "Blighty". Copper tubing 4.75mm (3/16 inch) is very popular over hear and seems to be what you are offered when you just ask for "brake pipe" at the local Factor (trade store) - it comes in 25ft rolls. Most of the local small garages seem to use it. Pure, unalloyed, copper is legal over here but not in some European countries or, I believe, in some of your States? It's big advantage is it's pretty soft, so flaring is easy with quite cheap tools being available and corrosion is not the problem it is with steel. It is easily bent to shape but work hardens easily so can't be bent more than once without weakening but can be easily annealed (resoftened) if necessary with a torch. I've read terrible tales of pipes which have work hardened over several years of vibrating on the vehicle subsequently shearing and loosing all the fluid. I've never actually come across this during my extensive life in and around the motor trade and I can't believe the British governing bodies would certify a product for use in this application if any real danger existed. So, as long as you buy copper pipe in a pack labeled as "brake pipe", I think it's fine. I tend to use it for short runs where a lot of twists and turns are needed and will say again that I've never seen a problem, even on some vehicles I've owned personally for 20 years or more.
For all other situations - long front to rear pipes for instance where copper pipes are likely to sag unless additional support is provided - I prefer Cupro Nickel. It's a bit harder so more difficult to flare and bend but holds it's shape nearly as well as steel so usually no additional supports are needed. You are likely to find that most "DIY" grade flaring tools will cope with it too. If I were to choose just one material it would be Cupro Nickel (often called "Kunifer" over here).
Steel pipe is actually quite rare to find readily available in store. It has quite a few down sides for the home mechanic, especially in regard to forming shapes and flaring. So, if you do manage to buy it you're then going to need a professional grade tool to flare it. Many of the steel products intended for use on braking systems are plastic coated to prevent/delay corrosion. A great idea but the trouble is you've got to scrape the coating off the ends so the forming tool can grip the pipe for flaring. Then the pipe rusts rapidly where the coating was disturbed making putting any sort of coating on it pointless in the first place! A pipe with no corrosion over it's entire length but heavy corrosion around the tube nuts is useless. I just don't buy steel tubing at all.
If you're going to buy a flaring tool look for one that can do steel tubing though. It'll last just about for ever on stuff like copper and Kunifer and it gives you the option of slicing into an existing steel pipe on the vehicle where most of that original pipe is in good order and flaring an end on it so you can fit a patch length to replace the little bit that was rusted. Also, on our vehicles over this side of the pond, most now have DIN form flares. Older vehicles had SAE. I wouldn't be surprised if SAE is still popular over there with you? If you were living over here I'd be recommending something like this:
https://www.frost.co.uk/brake-pipe-flaring-tool-set/ which has the considerable advantage that, not only will it "do" steel but can also be easily used on pipes still fitted to the vehicle.
Last word, If you're not going to get enough use out of buying a set of flaring tools for yourself many garages and factors etc over here will make pipes up for you if you can take them the old pipe. There's not a lot of labour involved - the difficult bit is shaping and fitting to the vehicle - so it can make sense to do it this way. On the other hand, if you've a lot of mates who "fiddle" with cars, you can make pipes up for them for a small premium and soon recover the cost of the tools - and make yourself popular into the bargain?
So, go on, buy yourself a good quality flaring tool - you know you want to! I get great pleasure out of making and fitting brake pipes - not quite so much trying to undo really rusted old ones! If you get good at it, lying under the car admiring the nice straight sections with neat bends and all nice and shiny new? Very satisfying indeed!
PS. As our Canadian friend has said above, I think those lines shown in the advert are plastic coated steel lines. If so you are unlikely to be able to bend them without a forming tool to bend them around. Like this sort of thing:
https://www.frost.co.uk/brake-pipe-and-tube-bender/ If you try to bend them freehand or round something like a screwdriver handle - which is possible, with caution, with cupro nickel and especially copper - the pipe will likely kink and collapse and/or sustain damage to the plastic coating. I especially like this design as it doesn't have a forming part which "wipes" along the pipe so causes minimal disruption to the sidewall of the pipe:
https://www.lasertools.co.uk/Product/6971/Brake-Pipe-Bending-Pliers Been meaning to buy one for years but never got round to it.
