the new springs are awesome in my humble opinion. I shoot the Gen4 a lot better than I do gen3.
The frame of the gen 4 is not only shorter by 2mm but also slimmer at the grip, which REALLY helps in customizing your grip with 1 of the 2 back straps if you need them.
Every person is different so you will notice some people shooting the G3 with no problems. I can't shoot them, they do not fit me and find the texture extremely slippery, which causes others problems in my grip. If I have to customize or add some extra rubber grip, the whole thing ends up being a 2x4.
The Gen4s fit me like a GLOBE, I use them with the medium strap.
Now, going back to the original topic. I really like the new spring (not that new really, it has been out for a while and it was originally designed for the mini Glocks). It was then used to solve some issues with G22 wearing a light, for some reason the old spring not only is weaker for the .40 but it was also having problems with lights attached to the rail. Note that the recoil spring in Gen3 is the same for 9mm and .40 whereas in Gen4 there are 2 different springs.
I do notice the recoil in the Gen3 when shooting 9mm but in the Gen4, not only the spring is a lot stronger and the recoil is inexistent but also the texture helps to keep the gun in your hands and by this you avoid fatigue. Fatigue build up turns into milking the grip (very strong hold of the grip/crunching it) and poor finger dexterity/trigger control.
Overall, I find it to be a really nice feature. It works for me.
I have tried shooting Gen3, they just do not work for me. Sold my last one not long ago.
I do not believe in aftermarket recoil gimmicks for many reasons, particularly because there are cheaper options that work: the gen4 recoil spring. I truly believe the gen4s are the perfect Glock.