The Xcelplus formula is now a concentrate... whereas the old formula was diluted in oil. Thus the new formula treats a ~7L vehicle. The old formula treated a much smaller engine ~3L (or less depending on the size of the bottle you bought).
The advantage of being a concentrate is that it is now compatible with ALL oil types (no oil incompatibilities).
Slick-50 dropped the price of the formula when they changed it from the original formula (I remember the price going down). Their new formula is the same formula that got them in trouble with the FTC ($10 settlement for false advertising). The reason they changed formulas was because of a dispute with their chemist (John Bishop) over pricing (they owed him $10M and didn't want to pay).
There's a video of John Bishop discussing this... look in the tests section. Plus there's a legal document mentioning this in the FAQ section.
The old formula used to treat a 5 liter engine just fine.
I had used it in a 5.0 Capri that I sold with 278k on it, never opened up the engine, and a 401 AMC Jeep I had built years ago.
The Capri would do 34 mpg on the highway all day long (2.78 gears).
And even if it increases my mileage 5% (unlikely) it takes way too long to realize the benefit of a Ben Franklin.
$50.00 a treatment would be reasonable but not $100.
Ignorance is lack of knowing; stupidity is false logic
Well that's a little dustup, or perhaps a tempest in a teapot. I was just posting up the Tufoil info because I personally have used the stuff for thousands of vehicle miles and they seem to have the same little old ladies taking my orders, i.e., bricks and mortar are all in place, unlike many other additive companies.
As far as the four ball test, Flouramics Inc, the makers of Tufoil, used to include a brochure in the shipping boxes with all the info on how they did it and where, but they seem to consider that a waste of paper these days. They also suspend PTFE in many different types of oil for many applications, which suggests a dedication to serving "all the industrial lubrication needs of the client", or whatever they say in their website.
20 years ago additives for oil became a fad, but Tufoil stands alone in my opinion as a real, measurable improver of FE and part life. Pretty easy to set up the four ball test: get the lubes lined up, a (drill) press and fresh balls and races. Have at it till the loser smokes.
NEVER under any circumstance put PTFE in a engine, NEVER DO IT!!! Teflon is great stuff but harmful for engines.
Been putting it in the same engine with 507K miles on it for the last 357K miles without any negative effects. The farthest anyone has ever been into the engine is the valve cover has been removed to replace the valve cover gasket and the oil pan has been removed to replace the oil pan gasket. (both done by me) Even though it has had PTFE run through it for years before and was driven on dusty constructions sites for about the first 350K miles and 12 years of it life the engine was still pretty clean all the way to the oil pan. This was also running 10w40 dino, never seen a drop of synthetic.
I wouldn't be surprised if the filter actually removes most of PTFE in the additive. Then there is also oil change interval. A short one, with filter change, would likely prevent the build up of PTFE.
These optional additives may not contain the the detergents, acid neutralizers, and other stuff found in a basic motor oil. Diluting them out will shorten the oil change interval. Or they have them in the wrong ratios. Some of the required additives have synergistic interaction with each other. Like dietary minerals. Your body can't make use of calcium for bone growth without the proper amount of magnesium, and a potassium level way higher than your sodium level will stop your heart. Throw the additive package in your motor oil out of whack, and you may have deterious effects.