Sinilink XY-WFMS
This device can be found on Aliexpress for about 5 USD.
Flashing

Can be tricky to solder the ground connection to the PCB due to heavy ground plane, I used P50 pogo pins in a printed adapter for 6x1.25mm but the Vin- screw terminal could also be used for conveient ground connection.
GPIO Pinout
| Pin | Function | 
|---|---|
| GPIO02 | Blue LED | 
| GPIO04 | Relay and Red LED | 
| GPIO12 | Toggle Button | 
| GPIO13 | Green LED | 
Basic Config
The following configuration is adapted from this ESPHome devices repository with only minor changes to fit the new device.
There is a 3D printable case available from https://www.thingiverse.com/thing:4638431 which I remixed from https://www.thingiverse.com/thing:4146127
substitutions:
  devicename: xy_wfms
  upper_devicename: "Sinilink XY-WFMS ESP8266 Wifi Mosefet"
esphome:
  name: $devicename
esp8266:
  board: esp01_1m
captive_portal:
# Enable logging
logger:
# Enable Home Assistant API (if available i.e. reboot_timeout=0s)
api:
  reboot_timeout: 0s
ota:
wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password
  #use_address: 10.0.0.230
  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: !secret ap_ssid
    password: !secret ap_password
    ap_timeout: 3min
web_server:
  port: 80
status_led:
  pin:
    number: GPIO2 # blue led
    inverted: true #off when ok
switch:
  # Relay (has red led hardwired; relay on = led on)
  - platform: gpio
    id: relay
    pin: GPIO4
    restore_mode: RESTORE_DEFAULT_OFF
  # green led
  - platform: gpio
    pin: GPIO13
    id: green_led
    inverted: false
    restore_mode: RESTORE_DEFAULT_ON
  #  # blue led (if _not_ used for status led)
  #  - platform: gpio
  #    pin: GPIO2
  #    id: blue_led
  #    inverted: true
  #    restore_mode: RESTORE_DEFAULT_OFF
  # Switch template to link relay and green led states
  # green led is on when relay is off
  - platform: template
    id: "${devicename}_relay"
    name: $upper_devicename
    lambda: |-
      if (id(relay).state) {
        return true;
      } else {
        return false;
      }
    turn_on_action:
      - switch.turn_off:
          id: green_led
      - switch.turn_on: #also turns red led on
          id: relay
    turn_off_action:
      - switch.turn_on:
          id: green_led
      - switch.turn_off: #also turns red led off
          id: relay
# Button
binary_sensor:
  - platform: gpio
    id: button
    pin:
      number: GPIO12
      mode: INPUT_PULLUP
      inverted: True
    on_press:
      - switch.toggle: "${devicename}_relay"