Hello.
The ideal caseback opener is just a rubber ball or something like that.
In fact, I know that 47mm VSFs have a caseback mm larger than gen, I didn't think that would also apply to 44mm models, but apparently.
If the situation is the same, then you will not buy such a key.
If for you the key, not the rubber, is a prerequisite, then
Hazing can to share his experience, he solved this issue on his own, as far as I remember.