Jasvboost - EGT, Boost, Bezel - $280
cobbler - No control unit needed. These are no frills gauges meaning no adjustable warn or peak functions(the Koso's have those functions), therefore they do not need a control unit. All you need for an install is some extra wire, and maybe a sandwich adapter that would add with installing the Oil Pressure sensor.
suzysube - Up do date.
imprezive one - Just to be clear, you do need a recessed pod like the one shown in the photo to maintain good contrast if installing up by the clock. Relative their price our gauges have good contrast during the day(for a constant lit LED gauge), but they are not adjustable like the Defi's(where you can turn up the contrast for the day. Price does make some difference
stentorian - If your thinking 4 gauges my suggesetion would be an AutoMeter Bezel mount and an ATi ePod. This keeps the gauges in the same general area making a full glance a bit easier. 4 Gauges, $399 (EGT plus any 3). ATi ePod add $119.95, Autometer Bezel, $59.95 = 579.85. As mentioned before you would need some extra wiring, maybe the sandwich adapter for the Oil Pressure sensor, and if you do Water temp you'd need need an apater for slicing a line if you installing yourself. If you go the route of Oil Press and Oil Temp you can use the same sandwich adapter.
turbo15 - easy of install. Otherwise you need to run a line from the galley plug(the sensor it too large for just plug an play into the gally plug) to the sensor and then mount/secure the sensor somewhere. Not a big deal for an installer though, but if you doing things yourself the sandwich can come in handy.
Here is a pic of the sandwich adapter with the Oil Pressure sending Unit installed(the wiring wasn't running too the sender yet though)