I just moved from my elapsed Optus 12 month SIM only plan to Jeenee mobile. Ported over yesterday. Jeenee uses Optus' 4G network.
The best options are (prices listed are monthly):
$8.98 for 5GB (first 6 months, then changes to $12.50 moving forward)
$19.90 for 15GB (for the life of the plan)
$24.90 for 30GB (first 6 months, then changes to $29.90 moving forward)
I moved from $36 a month for 30GB with Optus, to Jeenee's 30GB option. Jeenee uses the same network, so signal will be the same.
I called customer service once with a question before I signed up. Spoke to a local and didn't have to wait in a queue. I can't comment on post-sale support though, however I'd be surprised if worse than Optus.
No problems porting. I activated Tues night, and was cut over the following morning. Ports within same network take longer than to another network, however didn't experience any issues. Calls cut over about 1 hour before 4G was active, however that was expected. Only downside I can think of compared to Optus is no data pool option, and no perks program, if that's important to you. Neither are worth the extra monthly cost in my situation.
I would hop to Jeenee if slim hopping isn't feasible anymore.