>>64032342It's not an MP5-style charging handle, which actually has a decent amount of surface area for you to grip - it's a vz. 61 Skorpion one, where it's two charging "nubs" that you have to grip and pull back, which is pretty shit ergonomically
It was only done on the original SR-3 (and the Skorpion) to make it as slim as possible, so it could be carried concealed under clothing (or in a holster in the Skorpion's case) and you don't have anything sticking out and potentially snagging when you pull it out. Same reason for switching from the side-folding stock to a top-folding one, which doesn't double the width of the gun when folded up.
For the SR-3M, they were moving away from this concept (and desu, even as small as it is, it still seems of dubious utility to carry it concealed, although it'd look pretty cool to have something like the famous Reagan assassination attempt photo but with a guy whipping out one of these from underneath his coat), and more towards just an AS Val without the suppressor - so they essentially just reverted a bunch of the changes and went back to the regular Val features