I'm finding later on I only get 1 hit against my life at those ranges of health. I don't think this is of any advantage at all. A defense buff would be more useful... I mean it seems that reflexes starts at the overall lowest amount on toggles anyways... 12.5ish or whatever the guesstimate is.
As a scrapper I tend to go for bosses, as reflexes I tend to do well against them since I don't get hit... but against bosses and lts of +2 or +3 I'm going down in maybe 3 or 4 hits tops... I dont' think a "minor amount of resistance" that kicks in at 40% hps is going to keep them from dropping me often enough for it to matter.
And when I'm in a pack of minions, unless it's mixed with bosses/lts (which I have no business tanking as a non invuln scrapper) it's easy enough to jump out and run and recover. They're the only ones that dont' do damage in such large chunks for it to matter as much for the reistance. Practiced brawler already gives me the ability to run more often then not so it's not a issue with smaller damage amounts.
So yeah, to recap... neat sounding, save you a hit 1 in 10 times maybe, but mostly useless from my standpoint.