iShares Edge MSCI World Momentum Factor vs SPDR MSCI ACWI IMI

They track different indices: iShares Edge MSCI World Momentum Factor follows MSCI World Momentum and SPDR MSCI ACWI IMI follows MSCI ACWI IMI. They also differ in cost (0.30% vs 0.17% TER), replication (physical vs physical) and domicile (Irlanda vs Irlanda).

Nobody can know that: they track different indices, so their returns will diverge, and past index performance is not a prediction. What you can control today is the cost, the tax structure and whether the index actually covers what you want exposure to.

SPDR MSCI ACWI IMI has the lower annual fee. Applying the same 7% gross return to both with €300/month, that fee gap alone is worth about €2,414 after 20 years — that part is arithmetic, not a forecast.

Both are accumulating, so on this point there is no difference between them.

Yes. Unlike two funds tracking the identical index, these give you genuinely different exposure, so holding both is not automatically redundant — just be aware you may end up overlapping on the largest companies and doubling your rebalancing work.