I really wouldn't recommend housing an axolotl in an orb. I have owned one of these but found the filter not very good at all, and ended up selling it on within a couple of months, and i only kept tropical fish in mine!
When choosing the right tank for an axolotl you should look at the floor area, and not hight or shape or what may look nice. The bigger the floor area you can provide and axolotl the better!
A orb has very little floor area, and uses the very rough porous stone which the bacteria lives in. Because of the shape of the over all tank as well this really is the only filter option open to you as you would not be able to put a filter on the side of the ank, and also wouldn't look very nice!
Hope this helps!
