UltraGauge
PROs
-Affordable
-Easy to hook up and use
-Lots of guages (boost, batter volts, fuel trims, coolant temp, miles until tank empty, instantaneous fuel consumption, etc).
-Fuel cunsumption and trip-odometer can be calibrated to extreme accuracy (much better than factory) rather easily.
-Gauge design looks O.E.M. in a Sonic.
CONS
-Gets readings from the ECM. Not really a bad thing but it's readings are only as good/fast as the sensors.
-Digital readings. For some readings that change fast such as boost the UG is less responsive than a hardwired boost gauge because it only samples information every .xx seconds (it's essentially lagging behind what's happening).
Hardwired Gauges
PROs
-looks race car
-Faster response time
-Potentially better accuracy of whatever is being measured.
-Access to some gauges unavailable with an UG (oil temp, wideband AFR, etc).
CONs
-More expensive
-More difficult installation and running wires or vacuum lines and sometimes installing sensors
-Limited in the number of gauges that can be fitted in the car.