The ED uses low-dispersion glass so has no noticeable aberration. For me, the ideal eyepiece is the 20x or 27x fixed.
As Luke says, the initial impressions on seeing the scope will be based upon its diminutive size - can this really do the job? On picking it up, the build quality becomes obvious; on looking through it, best of all, it soon becomes clear that this is a serious piece of birding kit. The view is sharp, bright, contrasty and wide. A delight - so small, so light.