I know that Mec-Gar makes a lot of "Factory" mags for many of the big manufactures so the quality is there. Pro-Mag also seems to be a good mag.
With my budget one will probably be all I can afford for a while. I've always been a huge S&W revolver fan the only semi I've had was the Sigma and I like the feel(didn't shoot it much so can't comment on function) but the resale value sucked on ice.
I checked and the 5904 is 10oz less then the 5906 all stainless gun. Since it'll also double as a CCW gun that 10oz is huge for making a gun that's almost too heavy to carry vs one that'll work out ok.