Seems pretty hard to successfully pull this off. The better your chances of being successful, the more likely you could have gotten the offer on your own. If you needed the stand in to get the offer, you're not likely going to be qualified and won't last.
Perhaps it could be successful for people who are technically competent, but have a severe stage fright when interviewing. At the lease, you'd want the stand in to record the interviews so you could watch and learn who's who and get the context of the job before starting.
I dunno - to get jobs some places you need to be really good at leetcode - and that's a niche skill that is increasingly hard to keep current at as you get older, busier in your role and family life.
I'm not confident that I could do a leetcode medium anymore, but I am super confident I could do a similar role to the one I currently do at a company that would only hire me for it if I could do a leetcode medium.
I would never actually use a service like this but I can't say I'm not tempted.
Perhaps it could be successful for people who are technically competent, but have a severe stage fright when interviewing. At the lease, you'd want the stand in to record the interviews so you could watch and learn who's who and get the context of the job before starting.