Used to test guitar finish
I recently purchased a guitar kit with a mahogany body and maple neck, and decided to try a finish with Tru Oil. This is the first time I've done a serious woodworking project and didn't want to screw it up, so I wanted to try the finish on some test wood pieces first. Locating mahogany and maple scraps turned out to be harder than I assumed, especially smaller pieces that cost $20 or less each. The pieces from Woodworkers Source were exactly what I needed, and cost less than $20 together shipped. The pieces really helped me to get a feel for sanding and applying the oil, and gave an accurate preview of how my finishing process looks on the actual guitar.
The mahogany looks especially awesome with Tru Oil. It darkens up and reveals lots of interesting details. With maple, the change in appearance was more subtle. It goes from a soft white to more of an amber white, but does help to show off the grain. It also has a nice feel to it, which is the main consideration for a guitar neck.
Familiarity: I haven't used it yet