Mares usually like their udders cleaned. Especially in the summer when they get sweaty and sticky, it itches for goodness sake!
I used Excalibur for both the mares and geldings, it has cooling menthol in it and they seem to like it.
Even if your gelding doesn't seem to be dirty you should still do it to get the "bean" out. I won't get into details about that, just Google it - also some youtube videos about it. Also it's good to get them used to it for when they absolutely need it done.
But yeah, the mares dig it a lot - even my super b*tchy mare loves it. They are just like, "ahhhhhh, thanks!"
Some days it's not worth chewing through the straps.