The Portland Plotter is not used often in American sailing navigation courses but is the teaching plotter for the RYA in Britain. It avoids slippage problems with parallel rulers and seems more accurate since bearings and courses can be measured off meridians and parallels. It has built-in compensation for variation and deviation, if one desires. It is rather large which is both an advantage and disadvantage.
I personally prefer it because of slippage issues with parallel rulers and better accuracy with the scales. In summary, another excellent plotter that will suit some preferences better than others.