Sometimes the simple ideas are the best. The ones that become obvious in retrospect.
This simple little device comes in a package that claims, "Won't put your guitar out of tune!". Obviously the string tension has to be slackened in order to fit the device without damage to the instrument. Altogether it takes about 2 minutes to fit or remove, including re-tuning.
Depending on the guitar, it rests on either the nut, fretboard, or headstock. If you have an outstandingly expensive or rare guitar, you might not be happy with this. It works for acoustic or electric guitars, but works better on acoustic, I find.
It benefits from nut lube when fitting, as the alloy exhibits friction against the strings which tend to bed in, and more so than any nut I've encountered before.
This is a poor solution if you intend to intersperse fret-fingered notes with slide: the action is so high that the effort is hardly worthwhile and the intonation is ridiculously far off.
Otherwise, this is a very simple idea that works very well for either bottleneck or lap steel.
