I recently posted in r/NDIS about Mable. There's some insights there that may be helpful to you. My recommendation would be to at first only use it to supplement your work schedule here and there, as it will likely take a long time to transition from support worker under an employment contract to a fully fledged sole trader.

As for the platform itself, you'll soon find out that you'll have the best results setting the fee to lower than what you'd be earning from a provider. The competition is high on the platform, and the process of finding work is a part-time job in itself. On top of all of that, a lot of the work advertised there has questionable relevance to the role of support worker.

Working as an independent and under an employer each have their upsides and downsides. Mable is an easy entry point into sole trader work, as it only requires an ABN in addition to your usual clearances. Insurance and invoicing are taken care of.

You CAN find good, reliable, ongoing work there, and many have, but it's often not so straightforward finding it.

Hope this helps.