Awesome Jonny it gave ideas !
I will test a bit.
I wonder if it is not simpler to create a mathematical field and give a value based on range.
A kind of :
if tracker_field_value > 0 and < 10 = A
Else if > 10 and < 20 = B
Etc. Then I create a customSearch select with option="A,B,..." labels="less than 10, between 10 and 20, ..."
Cheaper and less complicate to maintain... 😉