they only as good as the sensors are and they are showing ya what the ecu is seeing, now if a sensor was fooked you and the ecu would be happy driving along when in actual fact there could be a problem but you wouldnt be aware of it as you are looking and the ecu is saying everything is all fine

so technicall a decent set of gauges is a beter idea, also using a secs to see what the ecu can see would be cool aswell