They are getting to be pretty reliable. That being said, I much prefer a mechanical lock. They are simpler, more reliable, just as secure, (if you don't give out your combination) and generally cheaper.
Some of the cheaper biometric locks made in China are a lot less reliable. Do your research.
But to me, biometric locks are not really needed or particularly beneficial in a household situation. They are far more useful in commercial uses where you have a lot of people requiring access.
For a home safe operated by one or two adults, a mechanical combination lock is a better choice. If you need fast access while you're home, simply put in the whole combination but the last number ahead of time, and you can get in with one movement. Reset the lock while you're away so the whole combination is required. Simple, easy, effective, cheap.
Here's some examples of home safes with the very reliable and secure Simplex locks:
Handgun Safes with Simplex Lock Mechanisms: Secure, Fast & Easy Access
These locks have been around for years and are still in use in commercial and high security installations. The combination is easily changed by the user, and some models allow for several different combinations.