Not trying to be offencive here...But you played with a TOY.
I'm assuming you are right handed & therefore would have the gun setup to eject spent shells to the right side.
The problem is when you switch to your weak (left) side your cheek will be so close to the ejection port that you will get smacked in the face with flying brass, Or you will cover the port all together & the gun won't eject at all.
You can pop off the back plate of the AUG and reverse the bolt so that it ejects from the left side, But this takes time you don't have in the middle of a fight.
Video, Note the ejection port
Their is also the issue of the offset site when you switch sides.
The only bull-pup that I am aware of that is ambidextrous is the FN F2000.
It uses a "shell tube" to push spent brass out of the front of the gun instead of the traditional ejector.
VIDEO
I would worry about the tube becoming jammed with empties & the gun quits working.
On a side note FN sells the F2000 to civvies as the FS2000, I have shot one (Along with a P90
).
I do not, & most likely never will, Have a piston upper for my AR.
I don't think they are necessary, Just maintain the gun & it will serve you well.
The H&K stuff is rare & VERY expensive, If you really want to go that route their are several manufactures that make piston AR uppers now. just check out
www.ar15.com
Again i'm not trying to offend you, Just telling you what I know.