is a haro f4 a very good bike 4 $500 aus

No, it's a very mediocre bike.

Not 100% 4130 chromoly
No chrome rims
But, it is a decent design and will last you a fairly long time if you maintain it well. It does have a cassette hub and smaller gearing a decent frame geometry. It should be alright.

i would not not buy it if you plan on riding hard at all. In september of 2003 i bought a Haro F5 and it didnt even last me a year.

Haro's are good for nothing overrated wall mart bikes