Pre-Uni, it's great to go to during your junior years, but i'd think thrice before thinking about enrolling at Preuni in years 11 & 12. I'm in year 12 right now, and i can personally say that despite for English (eventually dropped), IT IS NOT WORTH IT. They hire people who got over 99+ atar regardless of experience, a high mark is not an indication about their tutoring skills (introverted personality). I did English at Preuni, the only teacher i'd recommend going to if you're absolutely insisting on going to, is Mr Wills. His methods of teaching are orthodox and he's a great teacher (the only reason i ever went to preuni in my senior years). As Carrotsticks stated, price is low but that's indicative of their teaching standards. They've even started introducing humanities for tutoring which is rather redundant to be honest. Honestly speaking, you'd be better off going to another tuition or a private tutor. With that being said, everything is subjective; your choice.
PS. A pro for Preuni is that if you achieve really high in the final term test (top 10), they offer discounts. My friend's been going to Preuni purely because he's been getting 25%-50% for coming first all the time.