Edit: I deleted my old silly response for something more useful.
I don't understand your code; specifically, I don't get block_value, VALUE_A, and VALUE_B. I'll just state my opinions on the most comfortable "key holding", though: (this is oriented for typing, not games) it shouldn't be like "add another character every second held" or anything like that; there should be a pretty long pause between the first character typed and when the holding begins happening. For example, it should be like "after two seconds of the key being held, add another character every half second."