As for Helpful, I wouldn't work for a company that uses those sorts of recruitment practices. What they are doing feels very sketchy to me.
It massively balances the recruitment process in their favour. They are putting all the risk on to the candidates as they have much more to lose if they fail probation. I know from experience short duration jobs on CVs/Resumes raises alarm bells with recruiters. Plus, it could affect benefit entitlements too if they fail probation as that could be seen as a firing.
What if they have one position and decided to hire all five candidates on probation and make them compete against each other? That would be so stressful.
They could also misuse this process to quickly boost staff numbers for a short period instead of hiring contract staff.
It feels like the author is trying to use spin to make what is an unfair recruitment process sound like a good thing.