Hydrofluoric in more than a couple % is EXTREMELY DANGEROUS and you should be very well trained in its use. 8% is high and in this category. Can it be used to remove rust? SURE but the law of diminishing returns comes into play. It would not be worth permanently injuring yourself to do a job. And in actuality, HF doesn't work all that well and can damage many surfaces very quickly.
Currently we don't sell F9 in Australia and shipping is quite a bit. Your best bet would be to mix some Oxalic up and start with that.
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I currently already use oxalic acid now. Is it much different to Phosphoric acid as I haven't tried that on rust yet?