The Buttolo Blatter is the roe call most British stalkers end up owning. A soft rubber bellows, squeezed rather than blown, which means it works with cold hands, in gloves, and without giving your position away by the movement of a call to the mouth.
Three items here. The Blatter bellows call itself; the double-reed caller, which gives you more control over pitch and a wider range of notes; and the replacement ball for the Blatter, because the ball is the part that perishes and gets lost.
When to use it. Calling works during the roe rut — late July into mid-August in most of the UK, and later on higher ground. Outside the rut a buck has little reason to come to a doe call and you are more likely to educate him than shoot him.
How much. The commonest mistake is calling too often and too loudly. A short sequence, then a long wait. A buck that responds often comes in fast and silent, so be ready before you call rather than after. Wind first, always — a call that brings a buck downwind of you has cost you the buck.
Keep the bellows out of a hot vehicle; heat is what perishes the rubber.
Related: Deer Calls · Calls & Attractants · Stalking
