How long does the spring last? I had one like this with the offset holes for the wire clip and it popped out after 6 months from circular tension.

I've been using mine for a year and a half without trouble.

How wide is the eye, the closed loop part?

The closed loop is 1/2in x 1/4-3/8in however the clip comes with a titanium ring 1in diameter. There’s plenty of room for more rings in the closed loop. Both pieces are very light, robust and damage resistance. I’ve love the ring I actually bought another. I’m a Union HVAC worker and my keys are exposed to some of the most abusive conditions, I’ve had this for 3 months now and there’s zero discoloring or scratching. Highly recommended.

Is the spring wire of carabiner Gr5 titanium as well?

I have the “Gray” (non-colored non-plated/coated) version. Since the two answers given so far appear to not have much to do with the material that the “spring wire” part of this Carabiner Keychain is made from, the correct answer is: The main Carabiner and the included traditional round keyring parts appear to be Titanium, are the same color and are not magnetic in the least however I found that the spring wire part is very slightly magnetic and slightly lighter in color so my guess is that it is 302 stainless steel. Using a small jeweler’s file to round off some sharp corners of the 3 parts revealed that these parts are the same metal through.