Logic analyzer is a handy tool for digital electronics. But I wouldn’t say a “must have” device. So buying and wasting money for one isn’t a best way. If you need aren’t extreme then building out of available parts might be a solution. So Serasidis Vassilis made a tiny logic analyzer just for that.
Logic analyzer is based on AVR Atmega8 microcontroller and have four input channels each able to capture 400kHz signals. Signal waveforms are displayed on old good 84×84 Nokia5110 graphical LCD. Device is powered directly by four 1.2V rechargeable batteries giving total 4.8V. Simple but not the safest solution. So this is simple and helpful devices to have around.