The real problem with an "ordinary" PBN is...
Once a domain is included in the network, the PBN owner just sucks off the residual authority of the domain and starts selling outbound links to site owners.
Two consequences because of this...
1. The amount of PA juice passed gradually goes down over time until it does not even matter anymore.
2. Most of these PBN sites don't have traffic (and that means, no trust flow either).
3. Topical relevance is built not from general sites linking out to a wide variety of topical sites but only for outbound links to a specific niche of sites. E.g. IM-related sites linking out to IM-related sites.
Exception to pt. 3 — not all referring domains to a site are 100% related, so that's a part of natural backlinks profile. That's why the PBN links might work.
Then again, you will see some ranking improvement because something is better than nothing, right? (where the PBNs don't have footprints, do not have a spam history and at least the links get indexed over time).
The only solution I see is building your own PBN (which as
@GNews said is not really a PBN) or gaining rental links from "healthy" PBNs. In that way, the owner won't have to sell a bunch of links to maintain the network and would probably work on developing his PBN sites in a better way.
Frankly, unless you are sure how a PBN owner works or you know him personally as a person, it's not worth buying a bunch of $5/$10 backlinks from an anonymous service.
Anyone can buy a few high-authority domains from GoDaddy Auctions, host them on EBN and start their own PBN. The real challenge is maintaining the SEO value of the network over time.