Apart from the fact that it's almost a 100% fool proof way to secure your account, it also allows you to set one free teleport point. If those two things aren't worth keeping track of your number generator then it's not for you. There is an app for it, which I suppose can be hacked. However, I find it unlikely that anybody would go through the trouble of stealing/hacking a phone for the purpose of targeting your FFXIV account. So I'd say the phone app is just as secure as the key fob.