It's a couple Q's in on the page:

Q: How do I pay for Hyperspace? Hyperspace is a free download in the Mac App Store. Once downloaded, it’s free to scan an unlimited number of files. Scanning will let you know how much space is eligible to be reclaimed.

If you decide you want to reclaim that space, you will need to pay for Hyperspace using the purchase button that appears after a successful scan or by selecting “Purchase Hyperspace…” from the “Hyperspace” menu in the menu bar.

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alexjurkiewicz a day ago | parent [-]

It's four pages below the fold. The fact this is a paid tool is deliberately obscured.

	▲	goodmythical a day ago \| parent [-]
		Not sure why you're being downvoted. The fact that the payment is buried under 10k characters of text is deliberate. That it is not in the 'pricing' or 'buy' link in the menu where everyone has it is clearly a choice.