For sawbacks what to look for is for knives with no straight "saber-ground" flat surface below the teeths.
Ideally the knife should be flat ground entirely in one flat tapering surface on its side, so the teeth tops are actually wider than the rest of the blade, sitting at the base of a long triangle...: Original Liles are like this, and they still have the best working sawback in my experience: I compared that to the RJ Martin with a Parrish-style saw, and that is still a close second, even with a longer stroke.
Avoid United or Master Cutlery...
The performance I expect from a sawback, from my Lile sawback experience, is a 1.25 inch notch on diameters over 3" (it stops dead), and a maximum cut-through diameter of about 2 inches (small diameters really hugely help sawbacks). I never tolerate much time wasted, or much effort expended, so that is with not with a huge amount of effort at all...: Saws should work immediately with little effort...
The Martin Knives MCEII has a much enlarged Lile-style sawteeth pattern, and the performance I heard for these was an ability to saw through over 4" in diameter...: That required using a "rope-pulling" technique with a rope into the guard holes: I can't say I get it, but the claims are credible...
The TOPS "alternate leaning" teeth tops usually have performance-killing flat sabre-grind surfaces on the blade sides, but somehow they are aggressive enough to nearly match the Lile saw, similar in this to the Parrish/RJ Martin style, also sitting on top of performance-killing saber grind flats... The flats simply increase friction on wood, and eventually stop things dead...
A peculiarity to always watch out for, even for quality and reputable custom makers: Is the top of each sawteeths individually "dipped" towards the front? My Lile "Mission" was, but, to my astonishment, my Lile "Sly II" was not, and I had to have the work done by a sharpener for the saw to work...: Many custom makers "forget" this step: Some Steve Voorhies have it, some don't, the Andrew Clifford Sly II doesn't, and some of the "good" custom First Blood reproductions also "miss" that step: Without the "dip", a sawback will not even strip bark...
One weird alternative to "dipping" I saw was one teeth up, one lower, one up, one lower... I don't know if those work...
Gaston