It depends on how you use them and where.
For example, there's a bigger risk when building Tier 1 links with exact match keywords. Building Tier 2 links with non-commercial anchors, however, is considered very low risk. (SEO is never 100% risk free)
Having said that, here's a bit more information on the topic.
In general, using PBN domains is considered risky, because you depend on the PBN owner's knowledge of footprints avoidance. For example, if you purchase 5 PBN articles on 5 domains with the same IP address or WHOIS record, Google will just ignore these links.
But on the other hand, the cost of these articles can't be ignored, nor the speed of building them. Not all links need to be editorial, and that's why we've created this service.
Please note that QGP doesn't own any PBN networks or sites.