Previewed sells a licence. Ten dollars once buys commercial use and higher-resolution exports, and it keeps working whether you ship monthly or once a year. Its free tier exists but carries a Creative Commons attribution requirement, which makes it unusable for a commercial listing without paying.
Screenhance sells throughput. Templates and device frames are on every tier including free, so what money buys is how many exports you may take: three a month free, ten over seven days for six dollars, unlimited for twelve a month.
That difference in what is being sold matters more than any feature. Previewed's one-time tier is the cheapest way to own the capability outright. Screenhance's pass is the cheapest way to cover exactly one launch and then stop paying, and it is explicitly one-time with no auto-renewal, which the pricing page states rather than buries. Both are reasonable answers to bursty work; they simply disagree about whether you are buying a tool or a week.