I love my SMERSH, really comfy, loads of room and storage. Being ex mil meself, I too prefer not having anything on my chest. If I do, its usually a Chicom style rig purely for extra mags as a GBBR user.
Perhaps check out the 4UAS review of it on YT? They mention some of the same issues and how they rectified them. Explosive Enterprises are also good as is the Heavy Recoil Club Discord.
Oh sweet child of Summer, you aren't long on here are you? Avenger is one of our regulars in this thread...personally I would have banned him/she/it years ago...
Given the clown is also selling v3 AKM GHK mags with the feedlips already filed (GHK system is reliant on the feedlips being tight to get proper airseal, if you are getting jams its the BBs or your guidetabs on the nozzle not the feedlips, but I digress) I doubt he could upgrade his own arse with both hands. I have forgotten more than this clown knows about GHKs.
If the argument did hold water that the upgrade parts were worth full value its still doesn't account for £600 difference. But hey, don't criticise him!