[trextrex]

The original pre-print is available at: https://www.researchsquare.com/article/rs-3647379/v1

which is probably a less spammy source than the ResearchGate link.

[tetris11]

I'm surprised they chose Researchgate to publish their pre-print, instead of Arxiv

[dbcooper]

What's wrong with Research Gate?

[trextrex]

What value does it provide over linking to the original source?

Any website that constantly asks me to login is spammy in by book. It's a for profit website that adds little value other than duplicating information from primary sources and occasionally mangling pdfs with redundant information to advertise themselves.