I've been rather heavily involved in OpenEVSE - to the point that I've created my own variant of it (I rather cheekily call it OpenEVSE II), and I've met the Juicebox guys - even bought components from them.
I'm not in love with the juicebox design. The open-frame relay they're using isn't UL registered (so far as I am aware), and I don't believe they have a ground continuity monitor (again, to my knowledge). By contrast, an EVSE derived almost directly from OpenEVSE recently got full UL approval.
EVSEs are no joke. When things go wrong, they sometimes go spectacularly wrong. My own advice is to either stick with UL approved (or whatever is the equivalent for your country) EVSEs or become an expert on exactly how your EVSE works and inspect it frequently for early signs of problems. I like to build my EVSEs with transparent polycarbonate lids so you can see inside while they're operating, but that's just me.