The cheap testers only have a resolution of 1 volt, and only measure voltage and resistance. To be fair, probably 90 percent of the time a tester would suffice but the other 9 percent when you need current or temperature, or the final 1 percent of the time you need millivolts, farads and Hertz you're stuffed without a multimeter.
I had a Fluke 10 (voltage and resistance only) for years, it served me very well but no current measurement really let it down so I finally upgraded to an 87v last year, don't think I've touched the 10 since.
Admittedly part of it is it's just nice having the best tools, there's much cheaper meters than the 87v that will do everything I'll ever need but I was still considering benchtop Keithley meters.