I know we get loads of rubbish advertised (things you don't really need) but this is the limit - a burger holder. If you're that fussed, use your marigolds (as beloved by the late Mrs O).
Whenever I drive three miles up the road to my favourite burger van, the owner (Bianca) always cuts my burger into two halves for me. (I no longer have to ask her to do it; it's automatic).
She knows that I think it's far easier to eat that way, with the contents of the burger actually being eaten by me, rather than dropped all over the ground.
I'm surprised that fast food restaurants haven't also worked out that simply cutting a burger into two makes it far easier to eat!
I'd probably just modify one of them by cutting it in half. That way, after you've eaten half, you can transfer, with difficulty, the half-eaten burger to the 1/4 sized piece.