Growlers aren't really designed for the pressures associated with bottle conditioning. You might have a nasty, sticky mess on your hands if you use them. I'd suggest using grolsch style (flip top) bottles. They don't hold the volume that growlers do, but you can bottle condition with them and not have to worry as much about bottle bombs. The only growlers that I've ever seen that could hold the pressure are made with metal. If you store them long term, your brew can end up having a metallic taste to it. IMHO, I would only use a growler to transport homebrew to a friend's house. Otherwise, it is right out of the keg into a glass or into a grolsch bottle.