The EP moly additive is basically like the premium additive pack that is added to a base oil to get all the protection, viscosity, etc and many other things that the additive package does. One thing I can say from testing is that Schaeffers has what is likely the BEST additive package of any oil. This is basically that. The stuff is great for combating shearing as well as all the other additives used to combat wear, acid production etc... Its great is you a using a weak oil like Rot or any of the "synthetic" but not really syn oil which is most all of them other than Amsoil, a couple Mobile One, Schaeffer 9000, redline. Things like Rot, Valvoline PRemium, etc... are not real syn. Using EP moly additve even one bottle makes a dif. Its also only about $5-$6 a bottle. I have used it with my schaeffer 9000 5w40 for extend oil changes to combat shearing you get from HP HPOP pumps cause in all oils (ie 10K-50K OCI range). I use it for coating any new internal engine parts on install. Any new engine start up etc... I just installed a new Melling LPOP and coated it with this before installing it.
Rev-x is a blend of some polymeric esters from all that I can be find. These have some interesting lubricity properties as well as polar effects. From what is written you also need to use it with each oil change and the cost I have seen almost double to cost of a oil change. OOCH!! Also if you are running oils like redline that use esters you likely should not use this as there can be competing chemistry going on. The prior is from REv-x tech and what also points clearly to is being a polymeric ester blend of some sort. What turns me off a bit by it is cost but also the marketing claims they eerily echo those of Z-max additive which was/is a "similar" type additive and that company was actually sued by the FTC for false claims. But this is for sure a different company and likely a product.
Now with that said about REv-x from reports in the real world it seems to work fairly well. All you have to do is check out those that have had start issues in the 6.0 or even 6.7 and you can see its doing something positive so its not some snake oil for sure. How much does it offer a 7.3 with a somewhat different HPOP system etc got me. From all the postive claims its something you will notice with the very first use. This is good in knowing if it works as it costs a LOT so only having to use it once is a good to see results is a good thing for sure. Does it do ALL that it claims in the chemistry? Well I doubt it but it does seem to work from a laymans sense. I would say to see how much it really works start with a high quality syn oil like Schaeffer 9000 or even 7000 or some other of equal quality. Go thru two oil changes. Then on the next one add the REv-x and see. That way you are sure you have a good solid oil and the old is all but completely gone and the chemistry has settled in with the new oil. Now you will be able to see what it offers that no oils offer.
If you want the truth what I have found is its a combination of things that gets you the best results. What I mean by that is using a fuel additive along with using premium oils and possibly additive like Rev-X. The combo makes it much more noticeable. The diesel is this country is crap which is sad given the power we wield here. This is straight from the diesel engine manf and the diesel associate. Our diesel needs much more lubricity. Not to mention a few other things. I think combining fuel additive like Schaeffers Soy fuel additive ( it should be gallon to 500 gallon fuel or 1 12 oz bottle to 50 gal./ They have a typo in the premium additive description I believe and state 1 gal to 50 gal fuel which is crazy amount. All there additive are 1 to 500 per gal IIRC.) There are other good fuel supplements besides Schaeffer. I just use their products as I have found them to be for me the best choice from a performance and cost standpoint. They are very hard to beat IMO. Over the years I slowly (10-15 years) with testing switched to one of their products for each lubricant I was using ( Oil, grease, trans fluid, gear oil, fuel additive etc.)
You see the biggest effect in the winter if you live where it gets cold enough to get winter diesel. But I use it year round and see a 1-3 mpg effect. Even at 1 mpg change it more than pays for itself with the cost of diesel. Even without a mpg benefit the increased injector and pump IMO would be well worth it.
Combine this with a good oil setup and I think you see the best results that are more noticeable together than each separate. JMO