Given that today a lot of trade involve intermediate goods, an effective exchange rate based on GDP-weights is consistent with the Gravity Model that suggests an economy with a bigger mass will attract more trade, including direct and indirect imports and exports.
There are four aspects for alternative measures of REER which are (a) using end-of-period or period averages of the nominal exchange rate.
(c) in obtaining the real effective exchange rates, deciding upon the number of trading partners in calculating the weights.
One pair uses a "narrow" set of 27 countries with data going back to 1964, both in nominal terms and as a "real" effective exchange rate adjusted using consumer price inflation.
The "broad" set covers 61 economies, but with data only from 1994, again available both as a nominal series and adjusted for relative inflation.
[2] EER are still volatile over short periods of time and a poor guide for comparing standards of living across countries.