Yeah, this spot does look pretty good, but you'd really need a boat to get there if the wind was up. It's an inhospitable place when it's blowing a gale. I've been there in both calm and rough conditions and there is a lot of water movement in and out (mostly out due to freshwater flow) of the harbour and you've got Devil's Gate's right around the corner. The convicts built it as a breakwater, which is an amazing feat!! Could be a good spot for doing a NM. Despite the water movement, there's not a lot of tidal movement in Macquarie Harbour, with water levels more influenced by high and low pressure systems. During bad weather, the water level is usually quite high (low pressure). Here's a photo of a section of the breakwater when it's just underwater on a nice day.
It's these sorts of places we need to be looking for, that's for sure, just unfortunate sometimes how difficult they are to get to.
cheers