I use this flex hone on qt50 and other cylinders. Is it the best thing to use? I don't know but it has worked fine for me in putting a decent crosshatch on the cylinder walls. It just takes 20 seconds maybe and run the drill in both directions. A new piston and rings are so cheap, I would just go that route. Of course, measure your ring gap and adjust as necessary or run the ring expander under the 2nd ring if your gap is too far from the minimum spec.
And of course, you need to thoroughly clean the cylinder and ports after honing it. New rings require cylinder honing. You've got a bit of wear inside your cylinder and it looks like that piston has soft seized several times - both indications would strongly suggest that a cylinder honing is mandatory. Not sure why some pw50 guy with experience would say otherwise. I guess I could speculate - he was probably assuming that you didn't have easy access to a hone but who knows what he was assuming, right?
I've seen qt's running with similar and worse piston/rings/cylinders but since you've got it apart, it only makes sense to replace what you can.