I have a pair of ERC12s (the cardioid version of the ERO10) and they're decent SD condensers (in their price range). Though not as good as my Neumanns and Gefells, they are certainly in the same ballpark as AKG 451s or AT4041s.
You should try it out; the lack of proximity effect makes an SD omni a good contender for close micing acoustic guitar, mandolin, flute, piano - pretty much anything acoustic. Some kind of absorbent material (cushions, packing blankets, gobos, etc) set up behind the source (perhaps in a 'V' shape) should keep put the worst of the room reflections when close micing.
Scott