"Is there enough added nutrition in the "premium" product to make it worth paying four times as much money?"

Not enough to make any appreciable difference to any plants.

The hot composting should kill off pathogens in the manure product but I'd also want some assurances it was tested free of any persistent herbicides. Livestock feedlot compost (bedding materials, manure, hay, etc.) are more likely to be contaminated with these herbicides than is any sort of yard waste compost.

I noticed that neither compost had a really compelling amount of nitrogen. Why is it so many plants do so well from compost? It cannot just be about water retention and mulching? Maybe supplying just a minimal amount of all minerals as a background is enough to supplement other sources?

Fully agree with gardengal. If you've been adding compost for years, you may not need the P or K at all, and if you believe you really need the N, add just that. Would be cheaper too.

@armoured The surprise for me in those data sheets was how K is off the charts in compost.

You make me realize an important issue, which is that a loam soil probably has a high CEC, so over the years it may already be loaded on nutrients. It may not need much more than the trickle of nutrients in compost to stay loaded.

Yes, k - which used to be made by burning wood, hence potash - tends to be high in composts from woody wastes (which is going to mean most hot composts). High here being a relative term. You're right that you may not need much, but depends of course.

Oh I didn't complete that, the word potassium (k) is actually derived from the word potash.

@armoured That is interesting word history. But in terms of chemistry potassium is a basic element. Potash is a salt bound to potassium.

True - I wasn't claiming they're the same thing, of course, but emphasizing that the history is that our knowledge of potassium comes from plant forms (plant ashes). And in nature potassium is always found as a salt, so that's not much of a distinction.

Sorry for the language geekery but another part of this I just learned: in many languages (eg german, russian) the element is 'kalii' or similar, from the arabic for plant ashes, al-kalyah - which also gave us the elemental symbol K, the word alkaline and the term for the alkali metals, etc.

Anyway the implication for your purposes is pretty simple: if you've been adding a lot of compost esp woody composts (incl from hot composting) over years and years, it's quite possible you have plenty in your soil already.

I understand there are cases - perhaps extreme ones - of excess potassium in soils that have been really heavily composted. (I suspect where additional fertilizer also used as well but just my suspicion). That's where the argument gets complicated chemistry-wise, whether that 'excess' is in a form that actually causes problems or is bound-up in a non-harmful form - and I simply don't know enough on that topic. (Amateur linguistics is less dangerous to opine on than amateur chemistry)

Compost and manure are both soil amendments and fertilizers. They have a low NPK number but since this number is determined by weight and most of us apply more compost or manure by weight than we do fertilizer from a bag the number is confusing. When I use compost or manure I don't apply any fertilizer for the rest of that season and the next season can many times be skipped also.

Some "expert" needs to do a "study" and determine a comparison NPK number by evaluating the way the products are actually used. Inches of manure compared to pounds per 1000 sq ft for the bagged fertilizers. The problem with this study is that the horse boarder has no financial interest in a study to determine the value of the manure he's giving away free. And the fertilizer company has no financial interest in tossing away years of propaganda by "expert" gardeners.

@John D Zn6a PIT Pa Great points. I will create another post now based on this idea.