Flexi lines in place of solid introduce flex into the system where it is not required. This increases pedal travel and decreases pedal feel/sensitivity.

Buy about 4m of CuNiFe (Cunifer) lines and you should be OK. If you're going to do the work, it might be worth thinking about installing a brake bias adjuster and splitting the lines to a front/rear system instead of diagonal. Lose the rear bias adjusters, and fit stainless braided hoses between caliper and chassis (where flex is needed).