I want to grind flaxseeds, any good for that?

It does a good job on everything I've tried, but I haven't tried flaxseeds. It grinds fine as dust or coarse for pepper.Small and doesn't take a big space for storage. Sorry about not having your answer.

Why can't I get this thing open? I assume it comes apart where the white and clear plastic halves meet, but I've tried twisting,pulling, prying!

I had trouble opening this the first time as well. It does indeed come apart where the white and clear plastic halves meet; the trick is to twist it about 1/4 inch and then pull it apart. It does NOT twist all the way off. After the first time, opening it was not a problem.

I was hoping to use this grinder for dried hot peppers. Do you think it would work?

this unit would be too small for peppers. Check Amazon for a larger size that would work better. This grinder is good for small amounts only.

How do you change the grind to fine or medium?

I don't think you can adjust this grinder to medium or fine. It is meant to be used for grinding whole spices such as nutmeg, peppercorns or rock salt.