Don't buy credit card keys from eBay. You need the Virgin(unlocked) key from Toyota dealer.
The first time I got one from eBay, cost me $100, it's s***, didn't work at all, just waste me time. Used ones usually were programed before, someone can unlock it, but I didn't find anyone can unlock for latest version keys.
Regarding whether it is necessary to make a metal key, I think it is not necessary.
1. You can put a spare battery in the car. When the key is almost die, you can still open the door and get your spare battery.
2. The latest Toyota cars can be unlocked by mobile phones.
3. If you go to an uninhabited area, I think you can bring your previous Fob key as backup. The probability of both keys running out of power at the same time is almost zero.