groggy, nav tools are like screwdrivers: You have a favorite for any particular use, even if another one can do the same job. You really need to try out both tools to see which will suit you better, the same way that some folks can't stand mechanical pencils and some folks can't stand pencil sharpeners.
There used to be an inexpensive "Rolling Ruler" sold in the craft and hobby stores, stationery stores, and I think even Martha Stewart's scrapbooking line has something similar. So check the local craft stores, you may be able to get something under ten bucks that is plenty good enough for practicing with. Then if you want the better one...you leave one at home, one on the boat, it isn't a total waste to have two tools for this job.
yknow, that seems right. i like the idea of parallel rulers, but when i was trying to use them underway in 30kts, it was pointless. overall, i have settled on the portland plotter, partially because i of the ability to adjust in variation, and partially because i can mostly eyeball the vertical lines to the nearest longitude line even if it isn't lined up already, which it often is, without having to move it. it's a great tool.
i am learning to use whatever is at hand, especially as they are all kind of conceptually similar, but if i have to choose one tool to bring with me, it's going to be the portland plotter. and for aprox $20 it's an easy thing to toss into my sailing bag without too much cost or space or weight.
Mostly i use line of sight as i sail in a bay and can mostly just look and see where i want to go, other than checking on the chart for obstacles, and failing that, navionics with a glance at the charts... but I do like to plot on paper for fun.