Are there any caveats or benefits to TPI hacksaw blades?
It's a gimmick.
Since proper tooth size on a hacksaw is directly related to the thickness of the metal you are cutting, you are guaranteed to have 2/3 of the blade be the wrong toothing for whatever you are cutting.
Save your money to buy a better quality hacksaw frame that you can easily and quickly switch blades on, or get additional hacksaw frames and keep different toothed blades mounted in each one.
There is a different product of the same name that has some benefits in some situations - a &quot;Variable Tooth&quot; which is more of a slight variation (like 17-18-19-18-17-18 instead of 18) to reduce problems of harmonic vibrations from an interaction of tooth size and sawing speed. This is not the product you asked about, and it's of limited benefit for hand hack sawing where the user will simply adjust speed to avoid the vibrations.