Who does this feed?

[OneTonNoodles]

Birds or squirrels?

Ideally I'd like to fill it with food for both/either, that doesn't attract mice/rats.

Any ideas?

We have these for fatballs and both birds and squirrels eat from them. We have cats and foxes visit the garden so I’ve never seen a rat (there are mice in our semi rural garden but we only see them when they are brought home by the cats and not around our feeding spot).

Eating fatballs limits the amount of seed that falls to the floor compared to a tray or a more open seed or nut feeder where the birds scatter food to get the seeds they particularly like - and probably means you are less likely to attract any rats or mice.

If you have squirrels visiting, they’ll eat from any bird feeder and you will have to search far and wide for a feeder that will keep a determined squirrel out long term, if that’s what you want to do.

I had to stop feeding the birds as the vast quantities of food they dropped attracted rats, who moved into my shed. The rats never really went away until my neighbours moved and took their rabbits, and their rabbit's food, with them, but they did stop getting their dinner in my garden.
My parents have a similar problem with dropped bird food and "a little brown mouse" that's started exploring the kitchen. I've told them their little brown mouse is more likely to be a baby rat that's been sent on a recce but they're having none of it, although they have taken to sweeping up the mountain of dropped seeds each night which they say has helped

The neighbours garden that backs mine has had rat/mice. I suspect part of it is they have long grass they don't cut. I haven't seen any nor have had any in my house (thankfully).

There is a tray under the feeder I can clean everyday.

If I get a loose seed mix, will they just fall out of the giant holes?

Yes. That’s a fat ball feeder. You might be able to use suet blocks.