Given that you can get ransomware etc. from non-advertising content, let's say you are 90% protected from ransomware by using an adblocker. Turning the adblocker off momentarily for one site only probably reduces your effective protection level to say 89.9999%, in other words it does not significantly increase your risk, which is already significant due to the non-advertising based malware.
Ultra safe alternatives: Run Linux in a virtual machine or from a USB stick. Use the Chrome browser, which still includes flash support by default at the moment. No need for an adblocker as any malware will only infect the temporary OS, which contains nothing valuable and can be wiped after use.