I had Sky in an Aussie.. it's very secure and definitely fits more like an english saddle, but it does put your feet in a chair position because it's how the saddle was designed (for Australian ranchers and their scary jobs...) You can basically do flat in it, sitting trot was very messy for us and it wasn't as smooth as my saddle now, you can trail in it... and that's about it. It's great for safety reasons, or if you are going very long distances because it's both comfortable and durable..
But honestly I am glad I went back to my English saddle.. I feel so much safer, smoother, I can FEEL my horse underneath me rather than this huge bulk of leather and synthetics, I love my English stirrups and leathers WAY better, When I post on my English, I can really work my legs to stay where they are rather than using the little 'ears' on the Aussie and having my inner thighs whacked :P Eventually I stopped posting all the way up, just partly so I didn't touch the ears.
It's good for a nervous rider/horse or an unbalanced rider/horse to learn things like cantering or posting (not sitting trot...bleh!!) but other than that.... I wasn't so happy. Also the girth my Aussie came with had no elastic.. it's just leather on synthetics. I don't know if anyone else has the same girth, but urgh... no give besides a mm from the leather? I didn't like that at all..