What about manufacturer rebates?
Granny can always give you cash or just send it directly to you account in the same way.
The only time I really saw checks used was when I was a child ~30-35 years ago and my parents used them. I did once cash a check from an elderly relative, but that was very unusual and only happened once. I didn't even know it was still possible to do that, my reaction was more like if someone had handed me a stack of punch cards to run on my computer.
There hasn't been anything an average person used checks for in the last decades in Germany. Except a few elderly people, nobody uses checks and there are no rebates via checks at all.
Receiving a check however is even rarer.
As it turned out, my bank rejected both because they were made out to [middle name] [surname] rather than [firstname] [surname]. Ironically the former is unique (probably) whereas they had another customer with the latter.