how much does this hold

I holds about a cup. I bought it for coffee creamer which didn't work too well. Tried it with sugar and I use too much so it doesn't last long enough. It does work and has attachments to change from 1/4 to 1/2 or 1 teaspoon. If you use a small amount it will work fine.

Will it work with larger granules such as Stevia in the Raw?

I use sugar in the raw, and this sugar tends to clump (so it’s not free-flowing). I’ve learned to tap the shaker against my hand A couple of times until the sugar is free; then it works 90-95% of the time (sometimes I have to shake it again). surprisingly sugar granules do not get all over the place like you would think.

Does it work with powdered substances like coffee creamer?

It works with powdered substances like coffee creamer, However; the rising steam from hot brew gums up the mechanism quicker, a quick sweep with a small sharp instrument to dislodge clumps works for me.

What is the capacity ?

I think it is about a cup and a half or 2 cups...its really nice to control sugar from going all over the counter and is easy to refill. I would not be too worried about capacity unless you are baking and need a ton of sugar...in that case it would be silly to use this.