I've had a couple of these for years and they are handy for dialing in the fuel mixture. However the ones I have can't be used with the engine under load, like on a dyno or driving down the road, or they will blow apart
! My dad told me once that the hot accessory for cool cars way back when(like model T hot rods with no hoods) were sparkplugs made with glass bodys instead of porcelain so it looked cool when driving at night
! He couldn't recall any drawback to those plugs but remembers that it seemed a short lived fad. Leland