I am assuming you are taking about the pliers for plastic resin snaps that Serena sells? I haven't tried them (I have a press), but my understanding is that the pliers work well and are really great if you are just sewing diapers for your own use. The end result isn't quite as professional as that you get with the press (I've seen photos comparing the sockets in particular, with a press they will be centered every time, but it's hard to get them centered with the pliers, apparently). And I think the pliers are a little harder to get the snaps positioned.
Again, I haven't used the pliers, though. If she'd been offering them back when I bought my press I would have gone for the pliers for sure, they're so much cheaper! although now I do have the option of selling snapped diapers, if I can ever find the time to sew...