PLJ-8LED (clone) frequency counter: useful - but has issues

I got two of the wildly available PLJ-8LED frequency counter modules from Ebay. These are in fact clones of the real PLJ-8LED and one isn't working properly. As a little weekend project, I decided to put the good one in a little box and then show some of the problems you need to watch out for when using these modules. ... https://www.youtube.com/watch?v=WWy0821JLUQ