After deciding to tune my old piano on my own I first tried a low-budget solution from Amazon. The hammer did not exactly transmit my movements to the tuning screws of the piano and the results where therefore kind of poor and frustrating.
After switching to the K&M device even I could create an accceptable tuning for my piano.
The pro's will go for pro quality anyway, if you are a do-it-yourself guy like me, go at least for the K&M 167 or coonsider even more high end tools and avoid saving money here. You'll pay the price later with bad results, more frustration, wasted time, or buying a second device later.
If you are a beginner, make sure to order also the required muting tools (felt, wedges, ...).