Something a little odd here. The A-G 2300 should retail for much more than an Opus 27. The A-G 2000 or 2100 would seem to me to be more comparable models to the Johannus.
Sounds like the A-G is either a distress sale, or a used instrument.
In any case, I do not recommend buying an organ sight unseen. May save you a lot of grief, if it turns out you don't like it.