Since Be Quiet! Pure Power 10 series PSUs came out last year, it's much newer tech and it's easy to boast it over older tech: S12II series.
Reason why S12II doesn't have OCP (over current protection) and OTP (over temperature protection) is because when S12II came out in 2010, there were no requirements to have OCP and OTP on a PSU. Those protections that were required back then: OVP (over voltage protection), UVP (under voltage protection), SCP (short circuit protection) and OPP (over power protection), Seasonic also added to it's PSUs.
Still, because Pure Power 10 is newer doesn't mean it's better. While the 600W unit did fine in Tom's Hardware tests with some issues as well and some lower specs than S12II-520 (e.g voltage regulation is within 3% while S12II-520 voltage regulation is within 1%), what i'm more interested is the longevity of that unit. One way to know PSU's longevity is by looking the warranty period given to it.
If Pure Power 10 series would outlast S12II series (due to the newer tech), then it's retailer (Be Quiet!) would offer longer warranty than Seasonic offers for it's S12II series. Since Seasonic offers 5 years for S12II series, Be Quiet! should offer at least 6 years for Pure Power 10 series. But strangely enough, Be Quiet! offers only 3 years of warranty for their Pure Power 10 series. I guess Be Quiet! doesn't trust their PSU OEM: FSP. Then again, Seasonic is 1st grade PSU OEM while FSP is 2nd grade OEM.
As i said above, i have S12II-520 in use and i can say first hand my experience with it. My S12II-520 is currently 3 years old (bought it in 2015 as brand new) and it's still going strong in my AMD build. In one point of time, i used my S12II-520 to power my high-end Skylake build for few months as well. Used this time to also test C6, C7 and C8 sleep states since there's no official conformation if S12II-520 supports those or not. As far as S12II-520 fan goes, my PSU fan isn't noisy at all and i can hardly hear it, despite what is said in LTT forums (yes, i read that topic linked above).
With 2 years of warranty left for my unit, i can feel safe that my PSU does last at least another 2 years, if not more. And if anything should happen within the next 2 years, i can RMA my PSU without issues. But if i'd have the Pure Power 10 in use, it's warranty would be gone by now and when PSU decides to go sky high, i'd be left high and dry, without any hopes for RMA.
Btw, Seasonic still produces S12II series since it's tried, tested and proven to be reliable. Also, there are plenty of people in the world who still buy them.
For specifically about S12II series, this topic in JonnyGuru forums is a good read where many experts, including Seasonic representative, shared their knowledge,
link:
http://www.jonnyguru.com/forums/showthread.php?t=15009&page=4