Hot feet
To each is own and I agree the aluminum works as does 5606 fluid, but I think both of these are one step closer to a very hot fire.
The higher flash point fluids will reduce the chance of fire for sure. Granted the 5606 is easier to get, but than in several years of flying my RV, the brake system never need much service. Basically the need for a field repair is small. The 83283 fluid is not rare, any commercial FBO or service center has it. 5606 is only around because of the 60 year history, it has been identified as an extremely flammable fluid with a low flash point. Add hot brakes and....
Since we are building our own plane there is no need to follow the crowd for the sake of inertia, but that is just my opinion.
As far as flex line or flex brake line? Well if it does not crack there will be no leak and thus no fire regardless of fluid used. However if it ever does leak and you have 5606, you could have a bad fire. The cost, weight of using flex line is small to nil compared to the advantage. What I am hearing is a few folks have had good success with the aluminum line, one for 900 hours,while others obviously not. I guess by casual observation I have not heard of any flex lines breaking and therefore may be considered "better". Even if you don't have a fire a failed brake line could result in a ground loop if you are not aware of the problem.
IF you are going to use aluminum all the way, DO NOT bend it too much. Forming will work harden the tube (strain harden or cold working), making it stiff and more subject to craking and fatigue. I think Van uses 5052-O or 3003-O which is soft. If you really wanted to do it right, you could anneal the brake line after forming, but that requires kiln (oven) large enough for the whole line. To anneal 5052 you need to heat to 650F (775F for 3003-O) long enough to make sure its evenly heated and than air cooled. Some guys with talent say they can anneal it with a tourch. Since it must be heated throughout it would be hard to use a tourch on a long tube. The next best thing is just make sure you bend the tubing a min amount duing forming. You can also heat the tube to at least 500F to hot work duing forming, reducing strain harding. Caution if annealing a used line all trace of 5606 must be removed or you will have a hella of a fire, it is nasty stuff when too hot.
I mentioned some older RVs have nylon brake lines. If you have an old kit or bought a used kit or flying RV, you should replace the nylon with aluminum lines or flex line. Read the last three Par's in link below, RV-3 accident:
http://www.tc.gc.ca/civilaviation/systemsafety/newsletters/tp185/1-05/brakes.htm
Brake fires in general are not just a RV thing, many a plane have had brake fluid feed fire, some resulted in total loss of aircraft. Many of these are from the pilot riding the bakes during taxi.
The other part is of the equation is NOT getting the brakes hot in the first place. The BEST way to check you speed during taxi is use the bakes to get to a slow speed and than release the brakes completely. Allow the speed to build a little and then check the speed again. The brake, release, brake, release, method builds the least heat. The wheel fairing is very tight, and not a lot of air is going around the brake. So if you ever lean hard on the brake, for whatever reason after landing, especially from a higher speed, allow them to cool before using them again. G