It makes a big difference if the sawset is single action or double action! When you set the set on a tooth and squeeze the handle, depending on the gap between the plunger and the anvil, you can overset the tooth from the leverage on single action sets. Double action sets grab the saw plate first with a large plunger, then a second plunger comes out and bends the tooth over the specified amount.
The Stanley 42X is a double action plunger. This is a "pistol" type saw set. The Disston sawset is a "pliers" type saw set and it is also double action. The Stanleys sell for >$75 (I did get a pristine one at an antique store in Maine for $5!). The Disstons are much cheaper.
Both of these saw sets are really designed for panel saws. If you want to set a back saw, the second plunger is too coarse. However, both saw sets generally are assembled with threaded bolts, etc so that you can take the tool apart, remove the small plunger, regrind it to a narrower profile, then re-insert. I have two each of these types of saw sets, one ground for backsaws and one for panel saws.
The Disston sawset is excellent for backsaws because the metal back prevents the saw from being held adequately in saw vises, plus once you do get the saw inserted, there is no room for your knuckles to operate the Stanley sawset.
Another advantage of the Disston over the Stanley is that the Stanley bends to 15 degrees only. If you bend at the root of the tooth, you get a large set, if you bend at the top of the tooth you get a small set. The Disston has a rotating anvil with 4 beveled angles so that you can set at any given height 4 different degrees of set angle.
The new commercial sawsets are very cheap, and may work for a time. I believe they are aluminum with a steel plunger. Supposedly youcan get a panel saw set and a back saw set. Easier enough to do this yourself with a good steel Stanley or Disston, however!