Rigol, Siglent, GW Instek, and OWON have the best 4 channel Oscilloscopes under $500. I go over features like bandwidth, deep memory, FFT record length, screen size, ARB generator option, digital decode options, and various other features. These are the top low cost full featured Oscilloscopes.

GW Instek link
https://amzn.to/2OomVE0

Rigol link
https://amzn.to/2CCmjG5

Siglent link
https://amzn.to/2JGbdTX

https://amzn.to/2UaWDum

OWON link
https://amzn.to/2JDtvHS

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