All 4 ESP-01 have been tested with the flicker circuit and all work fine. So far I've made an IOT button with one and it's been working for a week now. You can find them cheaper but nothing beats 2 day shipping! I used a serial USB ESP8266 wifi module for programming along with a soldered button to enter programming mode.
TRENDnet TC-TP1 Network Signal Testing Probe with Adjustable Volume, Speaker and Compatibility for TC-NT2
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