Here is the theory with Evans (or any coolant for that matter)
First of all, discard everything you think you know about coolant temperatures. Coolant is the bucket in which heat gets carried away from the engine and dissipated in the radiator. The actual temperature of the coolant is only a factor in situations where the coolant boils. What happens with traditional EG and water is that it can boil at lower temperatures than straight coolant. People experience nucleate boiling at 230 degrees of indicated temperature, they blow a head gasket and get a warped head. From there on out, it is forever legend that and proof that 230 degrees can warp heads. This is far from the truth.
What happens is that the coolant mixture might be averaging 230 degrees at the sensor, but above the chambers it is beginning to boil. Everywhere its boiling, it doesn't have contact with water... which makes things hotter... which makes more boiling... which makes less contact. Then of course you have areas of extreme heat and areas that are still in contact with water. That is what causes the warping and head gasket failure.
The thought behind NPG is that when you remove the water, you remove the possibility of that nucleate boiling. At that point, the actual temperature of the coolant has very little to do with how effectively it transports heat. We're programmed to think that 220 degrees is too hot, but its only too hot because of the water in the coolant.
As long as heat out = heat in, the temperature will remain constant at or near thermostat temp.
One of the downfalls of NPG coolant is that it is not only less capable of carrying heat, it is slower to absorb and shed it. Its specific heat capacity is less than that of water, so depending on your vehicle, you may need increased airflow or a more efficient radiator to make sure that heat out is greater than heat in.
However, one of the points to NPG is that you can temporarily have greater heat in than heat out (increase in temperature) without much consequence. As long as your oil temps stay in check, (250 or less for conventional, 280-300 for synthetic), let the temperature rise. 300+ was a common thing to see in my Caddy 500 with Evans NPG on a long hill climb while towing.
Benefits: No pressure cap, so it has a greatly reduced chance of leaks or blown hoses. Increased lubricity for water pump. obvious benefits to rust reduction in the iron castings. No boiling. Hotter engines also tend to be healthier. Its so programmed into us to keep engines cool. We run cooler stats. The thing is, engines like to be hot (within reason of course). Without nucleate boiling, there are is less chance of detonation. That might be a nice benefit in a boosted application. When your car overheats and starts detonating, its not because 230 degrees is too hot. Those flame fronts are seeing 2000 degrees F. 10 more degrees of coolant temp isn't what is causing the detonation, its because the chambers have boiling coolant on the jacket. Its not the temperature of the chamber or the coolant, its because the timing advance is tuned assuming that the chambers and coolant are adequately moving heat away from combustion. When you get boiling, it can't pull that energy away and you get detonation. Put it this way... if you get detonation at 230 degrees with 50/50, that does not mean you'll get detonation with NPG at 230 degrees. The point is, without water to boil, Evans maintains constant contact and heat transfer regardless of its temperature
Drawbacks: When not running a pressure cap, you can experience a constant sweet smell of coolant. Without water, there is reduced heat capacity in the coolant so it may require increased efficiency elsewhere. Its expensive stuff.
It does have the nice benefit of not requiring an anti-cavitation additive in diesel applications. Diesel engines also tend to be much more thermally stable - larger capacity for coolant and oil, larger radiators, much more cast iron, etc. That is one of the reasons why its targeted at fleet applications. As you can imagine, a 3000-lb Detroit engine assembly that holds 19 gallons of coolant means that temperature rises would be gradual, but imagine a 1.5L aluminum 4-banger with a coolant capacity of 2 gallons. Temperature changes can be much more abrupt in the smaller engine.
As long as you understand that heat and temperature are linked but not equal, it makes sense. I liked Evans in my Caddy 500, but it wasn't really a big benefit. I can imagine it would be great in larger applications, but not a benefit in smaller applications.
You originally said, "So on one hand, it's got a much higher boiling point so there will be less chance of hot spots. But on the other, it apparently has 30% worse heat transfer than water, so while I may not be boiling it, it may not be cooling enough either..."
As long as its not boiling, and as long as it is not increasing temperature, it is cooling adequately. It doesn't really matter if its 180 degrees or 280. As long as you keep oil temps in check, it should be fine.
