they lose 50 max durability each time they are powdered. So you can add 10 durability 3 different times. the first powder on a splintering antiqe is really the only viable one. So you could powder when dura is at 190 and it will raise it back to 200 max. Something like that, i generally stay away from antiques so you might want to test for yourself to totally understand it. You also can not enhance antique so that is a drawback. On brittle metal you can enhance at 150ish to gain durability (metal only of course) Im not sure how splinter works with antique, if the antique mod effects the splinter mod and its a dura loss of say 30 rather 10 per splinter than its really not worth anything. I kinda doubt thats the case, but again best to transfer to test to find out exactly.
Basically, its a very good throwaway weapon. I wouldnt trash it, i also would expect someone to pay a substantial amount for it.