There are three basic systems. Anglo (Anglo-German), English and Duet. Anglos make a different note on a pushed button when you push and pull the bellows. English make the same note on both push and pull. Duet is a hybrid of both systems and is not recommended for beginners. Anglos are usually pitched in two keys (eg G and D) and are favoured by Celtic Tune players for fast palying across the keys in Jigs and Reels. English are used by Morris players, Shantymen and Singers. There are more buttons on an English Model but generally they are easier to learn and use for vocal accompaniment. All concs, old and new are expensive. Old ones may suffer from sharp pitch, duff reeds, leaky bellows and sticky buttons. All repairable at cost. Try "Barleycorn" in Scotland or "Marcus Music" in Wales. (Cheaper than Hobgoblin). A.C. Norman (UK 01825 713551) will make to order or advise on sources of second-hand.