I think they are electric. The back of the gauge only has 2 wires, and no vacuum nipple. I think it's specific only to S15's too. You can use the holder in S14's though, but you have to cut the top bit of the plastic to fit.
been looking around for an altezza this last few months..
(yup i know there some being sold in zth..)
some of the ones i've seen selling at the shops are bit run downed..(altho mileage...