Are free press release sites still beneficial for SEO?
Yes, but only indirectly
With the help of a press release, you can increase brand awareness or your product, get referral traffic that will improve your SEO
Most free press release sites have Paid options, you will benefir more from these sites if you can go the extra mile by using the paid options, as this will ensure you submission will be more widely syndicated to all their media partners site, and sometime you discover that most of the free services will not syndicate your press release to Google News which is key when using PR, but if you can pay a little extra you will benefit more from your Press Release submission as it will be widely syndicated to most of their choiced partners including Google News and others.