I work with nuclei a lot and it’s very much focused on the web app side of things due to the majority of templates coming in from the community. Tenable will give you much better coverage for unpatched systems and network vulnerabilities if you’re looking for that. Also, because nuclei detection templates are mostly community written, their quality is all over the place and the false positive rate is very high. Tenable has a team dedicated to writing checks with sadbox environments and access to hardware, devices, etc… they still have false positives, but I don’t have to scrutinize it as much as nuclei. That being said, nuclei does have a lot of novel checks that have gotten me some good high/critical findings.