I had problems similar to yours as well as the lights flickering when I got my 3 SF-01s. However when I went through the programming modes they became rough solid, except for 1 flaky tailcap. Try going through the programming modes and see if that helps.
And all 3 lights were dimmer with a new cr123 than an AA Eneloop for some reason.
The difference between high and low really isn’t noticeable unless one is paying close attention. Maybe yours came programmed as high only?
Mode changes are done on a half-press when the light is on and it has to be quickly done. For example when the light is off and it’s in high/low mode a half-press will turn it on in low and an immediate half-press will put it in high. Fully pressing the switch will leave the light on in high.
I’m definitely UI-challenged. As bad as this one is, it’s even worse that it’s not marked “SF-01” anywhere (mine are now) for when you need to search for instructions.
now i think my switch is flaky though - not debounced or something, i have it set to HIGH/LOW mode ( no strobe ), and it is still hard to pick the right one
I gave two of these away to friends. I didn’t even bother to tell them about the programming thing. I was thinking about just putting them into H mode only but decided on H-Strobe-Low to let them have fun. If they inquire, I will enlighten them.