I have had a yubikey neo on my keychain for almost 4 years now. It is thin plastic and seemed like it might not hold up this long, but it has been going strong. I think they have changed designs to make it smaller since (which would be stronger). They do make solid products.
That said, I would rather use Google Authenticate (TOTP) for two factor. Getting my phone out is a regular thing. Getting the yubikey out and plugging it in seems more of a hassle. Passpack is the only thing I have to use the yubikey for -- would be happy if they provided TOTP. Spending $40 for two factor these days is kind of ridiculous.
I regularly use 8 different devices (laptops and desktops). That's USD$400 in keys if I were to keep them in devices, not including shipping, currency conversion, etc.
Then there's the concern about who has access to those keys when I'm not around.
I keep a backup key in a safe location, and my primary on my keychain which is typically in my pocket.
That said, I would rather use Google Authenticate (TOTP) for two factor. Getting my phone out is a regular thing. Getting the yubikey out and plugging it in seems more of a hassle. Passpack is the only thing I have to use the yubikey for -- would be happy if they provided TOTP. Spending $40 for two factor these days is kind of ridiculous.