Bass Gear Direct is the store in Sydney, and I would take advantage of their 2 week trial period which they offer.You'd only be out of pocket for shipping which shouldn't be that much for a preamp that size, if you send it back.
I've got a Heart Rock and as others have said it is really full, detailed and 3D. I drive a Berg AE410/AE210 setup and it kills anything I have used in the past. Very useable gigging sound which gives you full control over the natural sound of your bass. I also agree that it sounds warm and even warmer than a lot of tube driven preamps. The input gain can be overdriven to the point where you get a very sweet natural break up of your sound unlike other SS heads which don't like being driven like that.
From what I know the Bass Art preamp is based on their more expensive Glock Bass Art Classic amp which is the flagship of all the Glockenklang amps. The quality of Glock gear is very hard to beat, built like tanks. One critisism of the Eden Navigator, I found the input very hard to drive to a decent level, don't why, couldn't get my head around how it was suppose to work, and I have heard the same from others as well. It does have a nice built-in compressor though.
Good luck mate!