For $35 most of the scope you see are going to be repurposed sound card chips acting as a digitizer. They work ok-ish but you get what you pay for. My big pro

For $35 most of the scope you see are going to be repurposed sound card chips acting as a digitizer. They work ok-ish but you get what you pay for. My big problem with a USB oscilloscope is that they are only ground referenced through the USB ground to your computer and if you measure something with a different ground reference you can blow up the USB port on your computer.