300K is nothing but a taste, for normal usage. I’ve been using NextDNS on my home network for a few years. I average 1.2 million queries/month. And that’s with cache boost (forced minimum TTL) enabled.
$20/year is worth every penny. The amount of time you save in blocking all the ads and surveillance marketing services is worth 10x that.
If you are getting something for free, you are generally the product, not the consumer.