They claim that, for instance, US companies raise much of their funding in the bond markets and the main channel through which QE has boosted the US economy is by lowering corporate borrowing costs. This effect would clearly be much weaker in the euro area.
Having said that, and although is still very early days, preliminary evidence (soft evidence if you like) on the impact of QE is really encouraging. The latest economic data and, particularly, survey evidence available up to March point to improvements in economic activity since the beginning of this year.