Sorry for the delay Jon...you know how it goes
Generally, there is no need to use additives at all...a well formulated oil has all that is needed. But to answer your question:
MPZ appears to consist of soluble molybdenum, phosphorous, and zinc dialkyldithiophosphate (ZDDP)...all are anti-wear/anti-corrosion/extreme pressure additives present in most modern motor oils. Moly is primarily an anti-wear additive...it's job is to reduce friction, therefore wear, in a motor. The most important thing to remember about moly is it comes in several different forms, a couple of which are not soluble in oil. These types are in suspension, and guess what, your filter is designed to remove particulates floating around in your oil. Use of insoluble moly in an oil additive is a very bad thing...you can clog the filter, it goes into bypass, and defeats the hole purpose of it being there. Soluble moly is a different story...it will not harm your motor and is the type oil companies use in their formulations. The big clue on moly is if the bottle says "shake well", run away.
Most experts on motor lubrication recommend avoiding additives, even though they may contain the same chemicals as an oil's add pack. Oil companies have spent a great deal of time and money developing the additive packs for their oils and they contain many other components other than the ones above. The idea here is the add pack is "balanced"...the effect of the various components are synergistic. That is, they react mutually in groups of two or more, to create an effect that none of them could attain individually. Changing or adding to this formula can upset the balance and negate the protective effect the formula was meant to achieve, even if you are only adding more of something that was already included in the initial package.
Think of it like a chili recipe...you add one habanero pepper to fire it up a bit. More is better, right? So, lets add 5 peppers to the mix...then you discover that you can't even eat the chili because it cauterizes your throat. Adding more of something in an oil formulation can easily have the same effect on your motor...you upset the balance and negate the effect the additives were meant to have in the first place. The same thing applies when mixing different types/brands of oils...if you decide to mix oils, make sure they have the same API rating (SL, SM, etc) and same SAE viscosity...avoid making your own "semi-synthetic"...don't mix a syn with a dino oil.
There are several other additives that contain the same ingredients as MPZ...Valvoline Synthetic Oil Treatment (VSOT) is almost identical. Mechanics Brand Engine Tune Up, K Mart Super Oil Treatment, and STP Engine Treatment With XEP2 contain ZDDP. VSOT is the only additive I would consider using and then only to restore depleted additives when doing extended oil change intervals (at the 15K plus range) and then only after doing analysis at 4000 mile minimum intervals to determine the condition of the oil.
While I'm talking about this, there's a few "snake oils" out there:
Slick 50 - Contains PTFE (Teflon)...the problem is PFTE is a solid. The hype for this is that it coats the surfaces in your motor, but reality is your filter removes it to the point of clogging up.
Bi-Tron & Prolong - I highly suspect both contain chloroparaffins...an additive most commonly found in machine oils. Great for machine oils, but crap for your motor. Chloroparaffin is corrosive at high temperatures. The chlorine is released from the carbon chain and forms resilient metallic chlorides in the surface of the metal...hydrochloric acid from disintegration causes corrosion.
Marvel Mystery Oil, Bardahl, Rislone, Lucas - These are kinda the opposite in the sense they remove deposits (including those put there by additives) and promise a "quieter, cleaner engine" or "reduced oil burning". Most of these products are made up of solvents and detergents designed to dissolve sludge and carbon deposits inside your engine so they can be flushed or burned out...kerosene, naphthalene, xylene, acetone and isopropanol are some of the solvents used in a base of standard mineral oil. They may have been useful in the '50's & '60's, but really have no place in a well maintained modern engine. They can be used to help remove deposits in an abused motor, but the problem is how much to use...personally I avoid these products.
Here's a little demo in a gear box on Lucas:
http://www.bobistheoilguy.com/images/lucas/lucas.htm
About the only thing I would use Lucas for is as an assembly lube...and that is because it's going to get dumped shortly after running the motor the first time
Here's a general rule of thumb on the way oil additives are marketed...if they rely on "testimonials", your warning light should be on...red and bright. This type of proof is purely anecdotal and does not stand up to any scientific analysis. You will not see any API/SAE certified test data...the reason you will hear is the formula is "propriety" and/or "is a cutting edge break through". There are no standards involved, it's individual perception, there are no experimental controls...the "believers" are going "witness" the magic...a magic that's simply cannot be attained by these or any other products.