Ummm, it feels really good, kind of like other forms of masturbation that do really cool stuff with neurotransmittors in your body???
Unfortunately, my fingers are a bit too short for reaching my prostate so I experiment with other items instead. My longest finger (index) is only 8cm long so reaching my prostate is not possible.
I finger my ass on pretty much a daily basis, or my gf will help me out with it. It helps me relax a ton (and moan) but i love it