Named our son this, but the problem is pronunciation. Many pronounce it "Coh-Lin" instead of "Cah-Lin". We chose the double L variant to reinforce the correct pronunciation.
To the person who said they named their son this and expected it to be pronounced "cah-lin", my name is this and it is pronounced "coh-lin". My guess is you are Irish however, because I was born in America. Pronunciation might be different there considering Collin is normally an Irish name.