They are really just a recording vacuum gauge. Google Filterminder. You install them in the intake tract, above the throttle and as near to the filter as possible (and away from a bend, as this can skew the reading up a little). There are various types, including dash mounted units. OR, you can simply use a vacuum gauge and a temporary test port, but if it doesn't record, you should have an assistant to record the peak number so you won't kill yourself gauge-watching.
Whichever type you get, for your purposes, I would suggest one with the largest range possible. Some of the recording gauges go as high as 30 inches and as low as 10. Vacuum gauges go as low as 5 inches and up to 30. If you go that route, get one with the largest dial face you can find and with the most increments (1 inch increments is ideal).
All of this only comes into play at WOT. For max power, you want the lowest practical number possible.
Whichever type you get, for your purposes, I would suggest one with the largest range possible. Some of the recording gauges go as high as 30 inches and as low as 10. Vacuum gauges go as low as 5 inches and up to 30. If you go that route, get one with the largest dial face you can find and with the most increments (1 inch increments is ideal).
All of this only comes into play at WOT. For max power, you want the lowest practical number possible.