I have the etekcity one. You can turn off the auto shut off. Doesn't plug in, but the batteries seem to last for quite awhile. It's worked for me.
You'll probably wind up with one of the two posted, just have to decide your price point and the features you want/don't want.
American Weigh LB 501
No auto shut off when plugged in
Comes with calibration weights
Larger/heavier than Etekcity
or Etekcity 500g
No plug in
Default auto-off, but can be changed to 1, 2, or 3 minutes or turned off
No calibration weights included