Callow used a clear, linear style that prioritised topographical accuracy. He focused on the structural details of buildings and ships. He preferred broad washes of colour over pencil outlines. His views of Amsterdam and Geneva show a mastery of perspective. He depicted city scenes and maritime subjects with technical clarity. His work avoids hazy atmosphere in favour of precise observation.

Modern collectors value Callow for his record of nineteenth-century European architecture. His prints of the Crystal Palace and continental cities show urban spaces before modern development. The clean lines and architectural focus suit contemporary interiors. These works offer a sense of order. They provide a historical perspective for the home.