Sharpen hand saw blades? Answered

.  +1. If you plan on sharpening blades on a regular basis, it might be worthwhile to buy the necessary tools, but, for many DIYers, it's more economical to let a pro do the job.
.  If you think it will be worthwhile to sharpen your own blades, there are many tutorials on the Web, unfortunately, I can't find any on Instructables. :(  Google is your friend.

My (perceived?) problem is the transition from the old -tool grade steel- saw blades to the tempered modern blades.

I assume tempered steel is not allowed be bent (the teeth would snap off).

Are you sure this ' saw set' tool works on tempered blades???

.  Not real sure. The whole idea behind tempering is to make the metal less brittle/more ductile. I'm no metallurgist but it seems to me that tempering should make the blades amenable to the slight bending involved.

This is a terminology glitch: I thought the proper word for 'hardened steel' was 'tempered'. When working in steel machining we did some hardening: heating in an oven, I think about 900 C, cooling in water (or with alloyed steel oil or even air) and subsequently re-heating I think about 500 C and slowly cooling down. This step was called tempering (Dutch: ontlaten). There was another procedure for re-heating to, I think 650 C, to make the steel less hard, but still very tough and strong (Dutch: veredelen)

No, I'm not sure at all but I presume it depends on the saw. I have always used older, cold rolled steel handsaws that were made to be re-sharpened, Disston, Sandvik, etc.
I acquired all of my saws more than 20 years ago, some from my Dad and the rest from various sources, new and used.
If I were looking to buy a hand saw, I would try to find an older one that still has some blade left. Making handles for the older saws is fairly easy, probably 1/3 of my saws have handles I made myself.