Now's not the time of the year to be calling roe. It only works effectively during the rut and even then there are no guarantees.
I've certainly had success with the Buttolo. The problem I have is that it can also good on muntjac. As others have said, the danger of using it outside of the rut is that all you're doing is educating the roe.
Back in 2010 I bought a Rottumtaler roe call (
http://www.stalkinggear.co.uk/index.php?main_page=product_info&cPath=21&products_id=146). It's more expensive and needs a bit more technique than the Buttolo, but it seemed to work a treat. I had a young buck come steaming in to the call from a couple of fields away. Whether the same would have happened with the Buttolo I can't say, but it certainly impressed me.
If you want to understand the different calls then I'd certainly recommend getting hold of a copy of Richard Prior's CD/cassette. Play it in the car and "fiep" along with it to perfect your technique.
Good luck!
willie_gunn