Q: Can Peer5 ever harm user experience?
A: No. Peer5 can never deteriorate user experience.
Q: How does Peer5 impact a user's upstream bandwidth?
A: Peer5 works with whatever bandwidth is free for upstream use and will not impact other applications that require uploads at the same time as Peer5. Changes to upstream bandwidth are unnoticeable to the end user.
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The concept is great, but until every consumer internet service comes with unmetered bandwidth, this kind of peer-to-peer CDN must be treated as what it is: a dark pattern from content providers who are looking to save their own bottom line while directly harming their customers in the process.
For every $1 a content provider saves by using this service, their users who happen to not have unmetered bandwidth will collectively pay dozens or hundreds of times that cost in overage fees to their ISPs. The fact that any business would use this technology and shrug their users' suffering off as an externality is disgusting to me.