Let's Back the bus up a second...
Ok there are a lot of unsubstantiated opinions floating around in this thread. If you are going to offer an opinion, state it as such. If you are going to state a fact, back it up.
Fact: Scratches, nicks die marks, and burrs will be removed from all hard lines because they cause significant stress risers. For tube systems less than 500PSI, the scratch limits in the straight section of tube is 15% of wall thickness. In other words, less than 15% deep damage will be blended out, more than 15% is cause for rejection of the assembly. Ref. older versions of T.O.1-1A-8 and now the T.O 42E1-1-1 (among others). And BTW, the damage limits are even less if found in the bend of the tube. That should just about cover the issue of whether tool marks are "OK" to leave in your tube.
Fact: "Paper thin", deformed, split, or over/undersized flares are unserviceable. Inspection criteria to determine serviceability can be found in a number publications (including the older versions of 1-1A-8 and now the T.O 42E1-1-1). We should not point to unserviceable examples of ANY system as justification for why they are good or bad. Hardlines, properly fabricated, installed and maintained, will generally last the life of the airframe - Even properly installed hose can't claim that distinction.
Fact: Flexible hose is a "specialized" product, generally used by exception. Because of it's expense, weight, bulk and yes, relative unreliability and fragility, it is used only when hardline can't be used. Examples include high relative movement between connections, or in some cases, to facilitate periodic maintenance (like engine removal). Aircraft designers go to long lengths to avoid flex line because except for a few specialized uses, hardline outperforms hose in every way. I doubt there is an aero engineer alive that dreams of someday building an aircraft plumbed exclusively with hose (..."if only it wasn't for the darn bean counters, I could finally do this aircraft right"...)
This information is simply common aerospace practice.
There are a few good reasons to use hose assemblies - but replacing hardline in a misguided attempt to increase system reliability is not one of them. Yes, that part is my opinion, but I doubt you will find an aero engineer who will disagree.
Bottom line: It?s your airplane and you are free to do what you want, but it is the responsibility of those of us who know better to point it out. If you want to ignore standard practice and blaze your own trail, at least be honest with yourself and the rest of us on the board. The danger here is that when it comes to design, most of the time there is ?right? and there is ?wrong?, and this is not decided by popular or personal opinion, politics, or a vote. It?s found in long standing, well documented engineering standards.
We all have a lot to learn? Let?s make sure we learn the ?right? things.