Full disclosure, I reserved this in a pinch when I couldn't secure a site within Joshua on recreation.gov, but I ended up finding the first-come-first-served (FCFS) sites within the park mostly available (late August at 4PM on a Friday). So, I actually didn't spend the night at Primitive Paradise. But, I did stop at PP before heading to the park and got the gist.
It's as advertised. It's a single dirt parking spot a few hundred feet off the main road with space to pitch a tent and a wind break. No other amenities. The pros are the absolute certainty of a place to stay and the proximity to services (food, gas, etc.). That's it. Given this, in my opinion, $25 is overpriced. But, it's an option.
For those in a similar situation, I would check with the ranger at the entrance for FCFS sites as they seem plentiful (if the right season), use the park's back country sites as a fall back (equipment and convenience not withstanding; they don't look like epic treks to the site), and then it's a toss up between PP and a Walmart parking lot. 🤷