Along the same lines, I just installed this one from Amazon in a recent build. At least the instructions were in English.
uniquegoods LED 4 Digital Tachometer RPM Gauge Speed Meter Tester 10-9999 RPM with Hall Proximity Sensor NPN Switch Red: Amazon.com: Industrial & Scientific
www.amazon.com
The VFD speed pot is integrated into the same Hammond Diecast box, I tap 2 holes in the back for mounting a L bracket. I typically mount these under the DRO if you have one, otherwise near the headstock away from flying oil and chips. RPM meter still has plastic covering on the display. Note that all these RPM gauge's hall sensor will only work with the correct magnet polarity, so mark the magnet as to the end that faces the hall sensor. You can check it by powering it up (can use a 9V battery) and then placing the magnet in front of the hall sensor and the LED light should flash on with the correct polarity. You can use electrical tape to temporarily hold the magnet to the spindle. Gap between the hall sensor and magnet is around 0.1-0.2", these use only one magnet. They are surprisingly accurate.