I have that exact model of TENS machine and it works very well for me.
Looks the same but I bought mine in 2017.
It still works, just takes a couple of AA batteries that last ages.
Took a couple of weeks although I noticed improvement within a few days when I used it daily, then I went down to weekly for a bit until I forgot about it for a couple of years.
I really noticed a massive difference after the first couple of weeks using it daily and I could basically stop worrying about any accidents.
Started when I had an uncontrollable cough and was at my wits end.
Got the same problem a few years later, pulled the machine out and it fixed it again.
I don't seem to get the pelvic exercises right, but this does them for me, or at least solves that issue.
It's basically silent and fairly discreet - you need to be sitting down so not really suitable for use while walking around.
I used it on all the different settings as I hadn't got a clue which I ought to be using.
Just sat down, turned on the tv and watched something while it did it's thing.
Couldn't really feel it much at first, but as it strengthened my muscles I could, so if you try one, give it time.
I went from fine but no trampolines, to having to use at least a pack of the heaviest Tena a day and change clothes, to needing nothing even on a trampoline.