Wonder what version openpgp their applet support, current app on Yubikey 4 and prior versions doesn't support ECC.
[0] https://www.yubico.com/products/yubikey-hardware/compare-yub... - "ECC applies to the smart card applet only; does not apply to the OpenPGP applet. ECC P256 is the key type generated for the U2F keypair."