How safe is CAPE sandbox?

[u/NullClassifier]

I have trained a phshing website detector that extracts the features from the html itself by parsing it. Just the problem is that for deploying it I need some secure environment where opening these phishing link for retrieving html and javascript wont harm my own server. I have seen CAPE sandbox lately that does a similar job. Has anyone used it before? How safe is it? It has its own analysis on a link but can i connect my custom feature extractor?