Why not use load and reliability K-values in EIGRP?

I'm trying to understand exactly how the load and reliability part of the EIGRP metric works and exactly why they aren't supposed to be used. The OCG CCNP ROUTE book says this on page 178 about using the load and reliability in the EIGRP metric calculation:

Also note that Cisco recommends against using K-values K2, K4, and K5, because a nonzero value for these parameters causes the metric calculation to include interface load and reliability. The load and reliability change over time, which causes EIGRP to reflood topology data, and might cause routers to repeatedly choose different routes (route flapping).

However, this site gives a completely different (opposite) justification for not using them:

First, EIGRP does not do periodic updates — only triggered updates. As a result, the values for Load and Reliability are calculated once when a route is first learned, but are not updated dynamically as an interface becomes more or less saturated. A change in Load/Reliability does not trigger a new EIGRP update.

And finally, the Cisco docs say this with no further explanation:

Although you can configure other metrics, we do not recommend it, as it can cause routing loops in your network.

So which is it??

Suppose I have a network like this:

A --- B | | C --- D 

And suppose that randomly now and then the path A -> B and also randomly A -> C have lots of traffic, it seems like having a way to steer A -> D traffic based on whichever side was less active would be a real benefit. Would adding the load K-value to the metric not do this appropriately?

I understand the problem of rapidly changing conditions causing excessive flapping, but there is a super obvious solution to that: just base the calculation on the average of a window, say 5 minutes, or 10 minutes, or something.

Is it just me, or isn't this super half-assed of Cisco to include options for load and delay but not a mechanism to send updates and control how often they get sent? If they don't work and should never be used, why the hell were they included in the first place, and why do I have to study them for the exam?