Good choice.
The gen4 and gen3 are both good guns. I prefer the gen4 design. Grip texture is better for me and I also like the enlarged magazine release. I don't care much about the dual recoil assembly. I have not had any issues with it, but I never had issues with the old style either.
For an extra $50 in most cases you get a 3rd magazine, better grip texture, bigger magazine release, and back straps to adjust it to your hand size. I don't care about the size difference, but I do like the beavertail backstrap and run the medium beavertail one on my own gen4 g19.