I woud certainly stay away from anything with a sawback. Those are at best suitable for notching, not for real sawing. If they are anywhere useful as a saw, they are dangerous for the user as you will be swinging a blade with sharp teeth aimed back towards yourself - if it bounces back you can get hurt. I had one like that (United Cutlery, I didn't know better at the time) and after I injured my off hand during light yard work I took an angle grinder and ground the sawteeth clean off.
My favorite machete is the Tramontina 14 inch bolo. It chops as well as an standard 18 inch due to the forward-weighted blade but it is a bit more nimble. With a good convex edge these chop like crazy, even in temperate hardwood (hazel, ash, oak saplings and branches as long as it is green; not for seasoned hardwood of course). They do come a bit rough, you need to put your own edge on and smooth out the spine at least. Some sellers in the States (Baryonyx? Machetespecialists?) can do that for you for a few dollars as a premium service. It also comes without a sheath. I got a Cold Steel bolo sheath, which is longer but can be adapted. It was the only thing I could find here in France. Otherwise, machetespecialists have sheaths for them so in the US you have more choice.
I agree with other posters, get a saw with it, any decent folding saw will do ten times better than a sawback on the machete itself. Silky is the obvious choice, if the machete is a Tram you'll have the funds for a good saw. With those two, any nasty growth will try to pull up its roots and run if it sees you coming. ;-)
Pics:

My bolo with the Cold Steel sheath, as it came (above) and after some adaptation. I put a short swedge on the front of the spine, with a steep edge angle so I can use it backhand fashion to chop at stuff close to the ground, or at roots. I also smoothed and rounded off the handle and added a lanyard hole. Note that the Tram has no scales, it has one solid wooden handle with a groove into which the blade is fitted, so your fingers curling around the bottom do not touch steel, there is no ridge there. Which also makes it easy to adapt the shape a bit.

The adapted sheath. I cut off part of the sheath's body while keeping the belt loop intact. It is quite flexible so you can use a paracord loop with a cord lock to fit it to your belt (or to whatever) as shown. The bolo, while still a large blade, can be carried on the belt this way as it does not come down to below the knee. It helps if you have less of a belly than I do... ;-)
Below: blade tip with the swedge. This is about how deep it goes if you take one wrist flicking blow at a hazel branch. In standing green wood, with a well-aimed blow you go through this size in a single chop.
