Will it work OK through a simple plastic case?
As long as it's thin enough and the charger is studly enough, as charging capacity drops quickly as the distance between device and charger increase, and wireless charging isn't all that efficient to start with.
Can I just leave the thing plugged in all the time?
Yes, but it will probably draw a small amount of current while plugged in without a device on it.
Can you leave the phone on it for extended periods of time?
Yes, but it may to more harm than good over time because heat is the enemy of a battery.
Can you use it to cook scrabbled eggs?
No,
but feels like it could cook an egg which is why I wouldn't leave a device on the pad for an extended time.
I'm sure some people do and don't notice any degradation in battery capacity or life.
I don't know that there isn't any, so I won't.
If you don't plan to keep a device more than a year or two, none of the above probably matters.
I tend to be more conservative, so YmAMV.
When a good man is hurt,
all who would be called good
must suffer with him.
Everybody matters or nobody matters.
You and I have memories longer than the road that stretches out ahead.
There is no safety for honest men except
by believing all possible evil of evil men.
We don’t do focus groups. They just ensure that you don’t offend anyone, and produce bland inoffensive products. —Sir Jonathan Ive
-An armed society is a polite society.
And hope is a lousy defense.
You make me pull, I'll put you down.
Mister, that's a ten-gallon hat on a twenty-gallon head.
I *love* SIGs. It's Glocks I hate.