I wonder if we're talking about the same thing though? I don't mean lines where the braid is on the outside - I can see that this could abrade other things. This is the company I got my Defender lines from - others are available: pioneer4x4.com As you can see, the braiding is internal to the line, so I can't see that they are likely to damage anything else very much. I think it's a combination of silicon outers, stainless braid inside, and a teflon liner. Maybe not available in your market because of legislation?
How long should it last? I guess maybe our conditions will be different. If I fitted new lines, copper and mild steel fittings, after the first winter, with the amount of salt on our roads (I'm in the north of Scotland) I'd expect the fittings to look rusty. After 2 or 3 winters there's going to be a risk of rounding things off during maintenance. The flexi hoses I took off the front of the car a few months ago might have been original (maybe not) but they were scrap. Not so much for the hose itself, but because the ends just corrode into unrecognisable lumps of rust. They might do the job while they are on, or attached, but as soon as you touch them they fall apart.
I'm not saying I'd fit them to the car and leave them 20 years, but at least when I did want to do any maintenance, I'd have a fighting chance of getting them off in one piece with a minimum of fuss and swearing.