I use a hands free leash as well and like it- the one thing to watch for is that if the dog suddenly wants to change direction you get yanked along with him/her (with a hand leash there's always the emergency option of letting go)- I've gotten used to this (I have a lab and sometimes she'll decide in an instant that she needs to dive down the bank on the side of the road to find the best spot to go to the bathroom) but depending on the dog, you could get pulled somewhere you don't want to be (like into traffic). The other thing to watch for is sometimes the dog gets close to you and the leash can go slack and be easy to trip over.

Have fun! (Despite the frequent pit stops and need to stop and smell the flowers- or the pee- I love running with a dog.)