which some say improves accuracy and others say cheapens the design.
The correct answer is it does both! Yeah, it's a cheaper construction method that doesn't look traditional or elegant, but it does improve accuracy - just like the Dan Wesson design from the 70s.
I have fired and considered buying a 620 and 520 (the short-run blued frame version of the 620). I decided to stick with my 686 (six shot). The interesting 520 I will buy when I find a good deal on one because it is unique. The 619/620 point a little handier without the full lug, but they also absorb recoil less well for that very same reason. Trade offs, Trade offs! My 686 is for powerful .357s, and for that I want recoil control and strength (hence the six shot, not the seven).
If you want a plinking/range gun you use with .38s and only shoot the occasional .357, then the 619 and 620 models are fine and accurate weapons. I am not implying .357 will harm them, but they will be less pleasant to shoot with .357 than the 686.
In this buying category, my "bang for the buck" gun is a used pre-lock 4" 686 six shot or 686+ if you must. Cheaper to buy now, and will be worth more in 10 or 20 years than a new 620 or 686 will be. Or try to find a good used 520, they will be novelties down the road.