I believe you are referring to EZ POOL. This product has been around for a while (and under more than one name). It it a proprietary combination product that has very little info available about what is actually in it but if you go to the manufacturers webpage there is some eye opening info. Their testing procedure for the oxidizer component in it is the same as the testing procedure for a non chlorine shock (which also needs to be dosed weekly, btw) and they also make reference to testing the copper levels which implies that this product contains copper sulfate. The caution about predissolving for plaster pools adds confirmation to this.
I suspect that the oxidizer in it is NOT MPS but sodium percarbonate just from some of the things they say on thier website. Two of their other products, while they don't list the ingredients, are used in the same way as sodium percarbonate (as a shock for biguanide pools and to convert biguanide to chlorine.) They do state that the bigunaide shock is NOT MPS.
I would stay far away from this product!
Also, there is no mention of EPA registraition numbers (not suprising since they only claim the product is an oxidizier and not a sanitizer) and there seem to be NO MSDS available for any of their products.
Here is some info on it from Poolforum. Pay close attention to what PoolDoc (Ben, the administrator of PF and TRULY the Pool Guru that got us ALL on BBB!) has to say about it.