Tom -
Here are the definitions on Frank's order form:
The Session Box – A great, no frills concertina, with the usual Edgley quality. Strong tone and ease of response. Stainless grills with flat finish. Available in natural domestic woods with natural finish, only.
The Performer’s Model – As above with polished stainless grills, bubinga, bloodwood, zebrawood, curly maple, sapele or other woods by availability. Natural finish. Excellent tone and response
The Professional Model –The ultimate in concertina tone and response, with angled reedpans, and choice of genuine hand-rubbed ebony, cocobolo, Indian rosewood, or other woods by availability. No other concertina, regardless of price or maker plays as easily!
Paul