These are my findings so far.
The ring is only recognised by the phone about 80% of the time. Just about acceptable, but hopefully that can be improved upon.
The lock screen isn't working well enough. Having tried a range of configs, I find the best one only works about 40% of the time. I have a PIN lock screen set and that is still displayed 60% of the time with the NFC Ring lock screen appearing after that has been passed. It seems that the NFC Ring screen needs several minutes with the phone locked before it replaces the PIN screen. Until that time, I have to get through both.
The option of using my Google email/password as an alternative to the ring is good, but it the password is visible when typed. Not good. Also, because it isn't using the password field type, it has added my password to my dictionary now. Really not good.
When my alarm goes off each morning, the NFC unlock screen come up but the ring never works. Seriously annoying.
In short, I would say that this is slightly below the reliability that I expect of a new App, but because this is a security app, this isn't acceptable. All of these flaws need fixing before I can accept that I can use my NFC Ring with any confidence.
So keep fixing the lock screen stuff and I'll keep testing it. Thanks.
Samsung Galaxy Note 2 - Android 4.3 stock. PIN Security. Three UK. Developer Mode Active. All Updates Installed.