$5.44 is a rebadged Schiwnn. This unit comes with a bigger LR44 battery. The Wally World is really cheap, but I suspect they still share the same electronics.

The $6.46 unit has more functions, including a stopwatch. Only downside is the vague buttons, and default to SCAN mode after wake from sleep. Both units are very accurate if properly calibrated...+/-0.5%.