Kawish,
I put one in recently and tore down top end last night for a 20 hr inspection and it looked new.
I followed the piston mods listed elsewhere in this forum and also the very specific break-in procedure in the complete top end rebuild thread by John.
This piston is the first time I used that type break-in. I know after 20 hrs of WFO MX riding I couldn't even find any scratches on either skirt. I do clean filter after every ride and throughly warm up engine before ringing it out plus cool it down before I turn it off.
Pros or Cons, I'm not sure. One of the senior, more experienced K5 riders will help out there.
Walter