“The Thumbie” is a cheaper thumb rest alternative to the ThumbsUp from Matchtechnical for Leica M8/M9 rangefinders:
“Made for the amateur or working professional the M8 M9 the ‘Thumbie’ has been designed to offer a secure grip while maintaining all the features of the camera and keeping them easily accessible. It is made from solid brass yet weighs only 13gms and shares the same tactile and visual qualities as the camera body, smooth, precise, and simple.”
“The Thumbie” can be purchased from eBay for £30.