The 'security' of biometric authentication is different to regular on a couple of major points.
Firstly, it is much more convenient than regular authentication methods. If 'who you are' is your password, you can never really lose it. A keyfob or pin code can be easily lost, stolen or forgotten, but your iris pattern or facial geometry are very difficult to separate from you (barring major accidents or extreme malicious intent).
Secondly, it offers a greater guarantee of non-repudiation. Say the security system were to open a safe containing money. If the money were stolen, and were protected by just a keyfob, it would be easy to assert that someone had stolen the authentication method from you from you rather than you stole the money yourself. A passcode gives slightly more protection, but could still be easily shown that the passcode had been stolen and used without your knowledge. If the authentication is your fingerprint, and you still have all of your fingers intact, it is quite difficult to prove that you didn't in fact steal the money yourself.
This second point is the cause of a real issue in authentication. If your personal authentication method is in fact stolen, how would one prove that you didn't steal the money? More to the point, if the authentication method is duplicated, how do you change your 'password'?
In terms of the security, it is arguably the exact same security using a fingerprint as a keyfob. Both would need a single item to be stolen to gain access. Same with a passcode. In terms of effort a robber would have to go to to gain access, a passcode would require the most effort (torture you to get the passcode), whereas a keyfob or fingerprint would require the exact same effort (steal something). Although the stealing of a fingerprint would be much more grisly (stealing your finger as opposed to stealing an item on your person), it's the same effort an attacker would need, therefore the same security.
Biometrics are generally best suited to continued authentication as opposed to initial authentication. Some item of data other than yourself is used to initially state who you are, then yourself is used to maintain access. This has been used in laptops with facial recognition software on the webcam. You use a password to initially log in, then the webcam looks at your face as you sit in front of it. When you get up, it detects that the biometric authentication is no longer in place, and locks the computer.
The situation you have described is still single-factor authentication, albeit using biometric authentication rather than 'standard' authentication. If using a single-factor authentication only, a passcode is a better option. If using multi-factor authentication, a keyfob and a passcode or a passcode and biometrics are better options.
What also needs to be looked at in your situation is the cost - both human and monetary. Any business should have insurance against robbery. Would you prefer that your store be robbed and your staff have a keyfob stolen, or that your staff have their finger/eye stolen? Also, is it really worth the money to fit fingerprint scanners when a passcode is just as secure as a password?
So, in answer to your question, on their own biometrics are arguably less secure than passcode authentication, more dangerous (to the owner of the biometric signature) if an attacker really, really wants to gain access, but slightly better at proving someone has accessed something if they say they haven't - until those biometrics actually get stolen, then they are better at proving you have accessed something when in fact you haven't.