i was doing this a while ago. i used a inexpensive radio shack digital meter, i think it sampled every .5 or 1 sec. fast enough concidering you don't want to be watching it that much anyways. your eyes really should be on the road... i ran a wire from the o2 sensor to the meter, under the hood and up to the dash. the only reason i quit using it one night at the track it started to rain, i didnt' take out the wire and the windshield wipers ate my wire.
if i was going to buy a meter for it i'd get an analog one so you can really watch it closely. or just a air fuel gauge, neither of these ways are overly accurate. and you have to watch out, there is a problem with where voltage is right. on a scan master or turbo link i think you want to be around 750 (i think...) and with a volt meter you want to be about 850.
if your on a budget it works, but if you can spend the money on somethign better, just do it.