HIO: Another point, the detector is kept stabilized by leaving it on. There is a possibility that when you turn it back on it may be a bit less sensative until it stabilizes again, plus by leaving it on, there is less chance of a thermal shock causing problems.
I leave mine on too...You won't ware the silicone button down.And battery life varies depending on how many targets you find and the headphones you use if any.
One thing to note if you use a DFX. It will turn itself off in about 15 minutes if the trigger is not pulled. It doesn't matter if you are detecting or digging. It just turns off. The manual doesn't tell you this but the "Digging Deeper with the DFX" does.
I have a cheap $50 kind I got at radio shack, it only has 2 dials, power and the discriminator. I hope to get a better one sometime but I can't afford it right now.