I bought my WRX brand new in early 2007.
2/24/09 @ 30,100 mi. = Drained coolant. Filled with distilled water only, turned car on and idled engine to operating temp, drained (process repeated twice since the water looked almost clear when it drained the second time). Filled with 50% OEM coolant, 50% distilled water, OEM coolant conditioner, and Redline Water Wetter.
8/26/10 @ 60,100 mi. = Same as above.
12/19/11 @ 86,300 mi. = While being protuned, the tuner noticed that my engine temp was not dropping as quickly as it should. The tech noticed that my overflow container was full of dirty gunk, so he cleaned that out really well and replaced one of my radiator caps since he suspected it was partially blocked by the same gunk. After that, the temperature dropped much quicker, so I immediately had my coolant system professionally flushed in an attempt to get as much gunk out of the other internal parts as possible. I suspect the gunk buildup was due to me simply draining and refilling my coolant and never actually having the coolant system professionally flushed.
It's probably too late for me to fully benefit from this product now, but it's probably something I'll consider if I buy another brand new car or build an engine.
Considering my most recent cost of replacing my own coolant:
(1x) 1 Gallon Subaru OEM Undiluted Coolant = $19.00
(1x) 1 Bottle Subaru OEM Cooling System Conditioner = $2.00
(1x) 1 Bottle Redline Water Wetter = $10.49
(5x) 1 Gallon Distilled Water = $0.83/ea. = $4.15
Total = $35.64
Since I've changed my coolant three times now, the one time cost of $43.95/gallon for the Evans coolant doesn't seem too terribly outrageous.