The Elite gauges aren't cheap, but they're really nice. They also have the ability to be a warning light (the whole gauge changes colors, and then flashes at the upper limit).
Being able to log exactly what the gauge is reading is also helpful.
+1
I went with the stack version, but they have the same feature set (high/low normal range set points, high/low danger range set points, multiple programmable relay outputs, programmable over/under/normal range guage colors, dimable, 0-5V outputs). Without the datalogger output you would have to install a secondary sending unit for the datalogger.
so, really its a guage plus 4 warning lights (2 low, 2 high), and a second sending unit, all in one. So, if you add up the costs of all the parts that are replaced by one guage the price tag doesn't seem so high.