Open assessment vs PSPO

Morning,

How different is the Open assessment compared to the PSPO 1 assessement? I understand that the PSPO is much harder, but the general advise on the forum is to do the Open assessments until you consistently get 100% and that is one of the indicators that you may be ready for the PSPO.

Is the Open assessment more in-line with the PSM one, as their are not many questions which deal with adding value?

I am consistently (last 10 attempts), getting 100% for the Open assessment, so how close am I to being ready for the PSPO? Or is there very little correlation between the two?

Thanks,
Justin