i have cunifer for my fuel lines mainly due to my concern of being able to bend 1/2 stainless. i wish i would have just gone with aluminum. in any case i wouldn't be concerned at all with the strength of cunifer. it's basically just like the copper tube you run in the house.
here is a picture of the color you can get out of cunifer with different types of polishing (hit the tube with three different methods here). it will probably need maintenance to keep that finish.
my main issue with it is that it still has a slight copper tint.
i did stainless for my brake lines about a month ago. it was a pain. it started as a prebent kit, but i had to make mods to install a proportioning valve, line lock and a residual valve. i ended up needing to make somewhere around 16-18 double flares. if you don't need to rework anything, then i wouldn't be concerned at all about stainless and leaks (once you get them tight).
i used a hydraulic flaring tool and even with that the tool was breaking down. i went through about 3-4 of the dies that clamp the tube. basically with a good double flare they will seal without much trouble. i had a lot of leaks but it was mainly due to not tightening down the fittings (mostly fittings and connections not related to the flares i made). everything was new or replaced on this car, so the odds of now leaks was slim. i used DOT 5 so i wasn't overly concerned about an leaks (peeling paint). i also had to remake the small curly fittings from the master cylinder. bending the stainless is easy with a torch (just don't cool the line quickly).
here is copies of posts i had recently made:
Mastercool kit 74175.
here is an example of the serrations breaking down. the one on the left was part of the first set where i did a lot of practice flares. the one on the right is after 2 flares (and tightening down the clamp more). The very first serration is showing signs of damage.
The more the serrations break down the more the tube is allowed to bubble up inside the grip area. this causes resistance in the tube nut or at worst case it won't even allow it too slide up the tube. It also causes the end to bubble less and have less material to roll during the last step.
on another note, i used a small torch to bend some of the tight radius on the tubes (where the small tube bender wouldn't work as well. that worked very well. some scotch bright and it looked like new. on one piece i did i put it under water to cool after heating and it seemed to become very hard. so basically if you heat with a torch, let it cool down on it's own. when i did they they still had a lot of give in the metal.
make sure the tube that's in the clamp is straight. if not the end of the flare won't be square.
i did several samples until i felt happy. i damaged two sets of dies during the learning curve. but it can be done. i had performed a lot of searches trying to find answers with an array of opinions rangeing from you can't do it to it's a piece of cake.
i probably did 10 or so flares before i almost think i know what i'm doing.
in any case here is what i did...
i start by using a fine hack saw and the back side of the die to cut off the line.
while it's still in the clamp i file it square and flush.
i then use about a 1/8" or so bit to debur the inside.
i simply used a piece of 220 on a D/A to scuff the outer edge. this is the result.
i then clamp it in. i used a piece of tape to monitor if it was being forced back out of the die. i think clamping it really tight might help prevent the clamps from breaking down so quickly.
it's then ready for the final step. i use just a little grease on the tip.
final result. i split the stainless on the very first two flares (careless prep, didn't know what i was doing, started adding grease, etc)