I used
LeFrenchMobile and it worked out great. Very easy to configure (only thing I had to do was add "mobiledata" to the APN entry) and worked as well as any other roaming option I've used. I think it uses Telstra's network if I recall correctly? I think that's what the network indicator said.
Topping off is easily done from your phone. Works for two weeks if you don't register it, much longer if you do. Initial card is 19 euros with 1 gig of data; 3 gig to-off is just 38 euros. The only weird thing is that you can't add to that 1 gig until it's used up.
3G, not 4 or LTE, and in rural areas, sometimes drops to EDGE. That's the norm for most/all networks, but coverage has been improving greatly over the years. I'll definitely be using them in the future.
Hope this helps-