Hi Christos,
In effect, buying a hedged product (like the CDRs) effectively means that it takes interest rate fluctuations out of the equation. Typically, when the CAD rises in valuation relative to the USD, then a hedged product will result in higher returns & the opposite is also true.
In the case of CDRs, they have what is called the CDR ratio which measures the # of underlying shares the CDR owns. It changes on a daily basis and if the CAD rises in valuation relative to the USD, then the CDR will represent a larger # of shares. If the CAD weakens, the CDR will represent a smaller # of underlying shares. If you bought NVDIA on the US markets with USD and say that book value was $1,000, if the CAD strengthens and the share price stays the same, your market value in CAD would effectively decrease and you'd own the same amount of shares. That is because of currency fluctuations.
Let me know if that helps explain the difference.
Mat