I'd agree - I think if you have heavier rust, it has to stay "wet" for at least 15 minutes for a phosphoric acid to make any difference.
So if you've got a lot of heavy rust, you'll be in the poor house in no time using picklex.
Not the right product for the job.
Sandblasting/wire brushing is the right product for that job.
Minor rust - be sure to let it stay wet for longer than you would clean metal.
On clean metal, just spray it on - wipe it thin with a cloth or brush and let it dry.