DO NOT WASTE YOUR MONEY!
I spent 21 years in Shell Automotive Lubricants division.
These oil additives are 'Snake oil' .
With modern synthetic oils you do not need them and all they do is unbalance the additive package that the 'proper' oil companies have spent many £1000's perfecting.
The diagram of the 2 steel billets (on their web site) showing wear is a con.
I actually caught an STP salesman trying to sell his product to a Shell dealer. He had a special rig that put extreme load on a steel billet like the one shown. With ordinary engine oil (at the time) he got the severe damage shown, dripped some STP into the oil bath and it looked like the second one with less wear.
I opened a bottle of EP*90 gear oilm and dripped it into the oil bath and the wear was LESS than the STP showed.
STP was simply an extreme pressure additive (EP*)
I suspect that the basis of ZX1 is similar and it ain't cheap. £54.99 a LITRE You have GOT to be joking!
Don't be conned!