It's not very well explained through text, my apologies. What I mean is, one tap selects the item on screen (in this case, the digits on your lock screen), then once its highlighted, a double tap (anywhere on the screen) is required to execute said selection.
I'd recommend playing around with this type of operation in the app before you enable it to take system wide control, to ensure you know how to operate effectively. However, unless you're visually impaired, this app won't do you much good anyways.
However, I do not think it's fair to down rate a perfectly fine piece of accessibility software, for what appears to be your mistake. If it's genuinely a bug, then it's acceptable, but it seems to me this is a case of operator error.