We use both.
For PKI, our Rubicon Identity Service is the fastest, easiest way to provision PKI keys to IoT devices.
For devices too small, inexpensive, power or memory constrained to use PKI, our symmetric approach is the perfect solution. We use symmetric algorithms (SHA-2,3; AES 256) that are NIST-certified just as the RSA and ECC algorithms PKI depends on. Once quantum computing becomes real, symmetric crypto will remain robust while PKI algorithms will be hampered. For IoT devices in the field for years (smart ag, security, payment terminals etc.) or decades (automotive, industrial), this is a huge issue that Rubicon solves.