Backsaws are lovely beasts. Brand seems to be less important than overall quality, sharpness, and suitability to the work at hand. Many of the cheap saws are light which really works against the user.
Cutting tenons normally requires crosscutting for the shoulders and rip cuts for cheeks and haunches. Having said that, sharp fine tooth saws with rip pattern teeth (up to about 12 teeth per inch) can perform both cuts really well. As I understand it, it has to do with the size of the teeth relative to the fibers of the wood. Larger teeth have larger gullets which helps to carry the sawdust away when sawing wider sections, such as in most tenon cheek cuts. Likewise, longer saws are more efficient for wider stock because you have more teeth engaged in the work and the longer stroke helps with the dust removal. The other main factor is the depth of the cut. Obviously you have to have enough depth to your saw plate when cutting the cheeks of long tenons.
I would recommend you look at the sizes of tenons you will probably end up making based your work and how important speed and surface quality of the finished surface is to you. The requirements for small scale work are vastly different from timber framing or building Roubo benches. I have several saws and have found that a standard sized (10 to 12 inch long saw plate) rip tooth (14-16 TPI) “dovetail” saw will manage most of my tenons. I do have several “tenon” saws that I generally don’t keep at the bench full time. They are generally 12 to 16 TPI with about 14 inches of saw plate. I have them all filled with rip teeth just because I find little, if any, advantage to a crosscut tooth profile in my work except for courser (than my bench saws) panel and carpenter saws. There are some “better brand” crosscut saws at the bench, but to be truthful, the little difference in the quality of cut across the grain means that they get little use. The “tenon” saws see duty for larger tenons because of the plate length/depth and when I want a saw with a thick plate (those grandkids love to saw are rough on thin plate saws). I generally assemble straight from the saw but will, occasionally, use a router plane or a rabbet plane for fine adjustment. If you prefer to use those tools on your tenon cheeks regularly then the surface finish from the saw becomes even less of an issue. I would love to see a joint strength test conducted based on saw produced textures as opposed to other tooling techniques.
There is another option that I use for really large tenons. I take long miter saws with around the same number of teeth as my tenon saws. filed rip. The extra size helps with the extra sized tenons and the extra weight helps with the sawing process. The larger, heavier saws can be harder to get started under good control and it really helps to establish a good knife wall in the initial stage.