Gondola Holdings is to replace its Jo Shmo's American diner brand with Byron, a new casual-dining burger concept. The company, which also operates Pizza Express, ASK and Zizzi, is to convert existing Jo Shmo's outlets in Guildford and Kingston-upon-Thames to the new restaurant format after successful trials at the first site in Kensington, west London. Harvey Smyth, Gondola's chief executive, told M&C Report that the company was also looking at other locations for Byron, although said any roll-out would be measured. "We are not in any rush with this," he said. The first Byron had exceeded the company's expectations. The Times restaurant critic Giles Coren recently described its flagship menu item as "probably the best burger I have ever had". Jo Shmo's was launched about eight years ago but was never taken beyond three sites. The third site - in Wimbledon, south London - was recently sold to Dominic Ford, the entrepreneur behind the fledgling Butcher & Grill concept.