I recently purchased a SP9A3S with curved mags, SBR'ed it with the factory folder, and installed the 40 degree. In terms of recoil, mine seems quite different from what others claim in this thread and elsewhere on ARF, especially in comparison to a MP5 type.
1st, I shot it side by side unsuppressed using 115gr with a APC9 SBR and found the Stribog definitely softer, as expected. Not by a huge amount, but it was obvious enough that I'd put them in separate groups.
Later, I shot it side by side unsuppressed using 115gr with a Kriss SDP SBR 9mm with a .45 slider and recoil spring, and they felt very similar, hard to tell apart, and I'd group them together.
Later still, I shot side by side the Stribog unsuppressed using 147gr with a MPX-K SBR with a custom gas plug and suppressed with an Omega 9K (short barrel, long hand guard, tucked suppressor and I didn't want to remove the hand guard) as well as a SP5 SBR unsuppressed with an 80 degree locking piece. The MPX-K and SP5 felt very similar, hard to tell apart, with the SP5 being slightly softer. The Stribog recoil was stout and harsh in comparison to either of them. I'd group the MPX-K and SP5 together and the Stribog in a separate group.
I know, I know, the SP5 weighs more, unsuppressed vs suppressed isn't fair, blah, blah, blah. Regardless, my experience seems quite different to others. So much so, I'm curious if some actually compared them side by side, or are just going from memory, or who knows what.
I have some ideas I'd like to try with the Stribog locking block. I'd also like to get a 35 degree to play with. So, if anyone has a friend in Norway, where I found a vendor, or a lead on one, please let me know!