Some locomotives were equipped with small wooden tenders to carry extra coal.

[1] The locomotives were designed to operate at low speed, shunting heavy loads, on tight radius sidings and points.

It seems that having trailed a small number of locomotives built by Neilson & Co, each railway company was given consent to produce further examples itself, under licence, happily attributing the design to their own respective Chief Mechanical Engineers, Dugald Drummond (CR), and Matthew Holmes (NBR).

[3] Having obtained license to replicate the design, each of the railway companies incorporated minor detail modifications into their version.

The Great Eastern Railway Class 209 is similar but has a flat-topped saddle tank.