Bleeding brakes and mixing fluids

I am soon going to be doing a disc and pad change and will also be bleeding the brakes.

I have half a bottle of Toyota DOT 5.1 fluid, which I would like to use.

Since there is only about 3 litres left, I will need another bottle.

Do I have to use Toyota DOT 5.1 or will any other DOT 5.1 by a half decent manufacturer be ok?

Is Toyota's DOT 5.1 same as anybody else's or should I not be mixing Toyota and brand X?

I've read somewhere that it's always best to use "fresh" bottles as opened ones absorb humidity hence reducing the boiling point. Not sure though.

All DOT specifications specify the minimum boiling point. There are DOT4 (like the Catrol SRF) fluids that have higher boiling points than some DOT5.1 that just meet the minimum spec.

I you don't intend to track the car I'd say an over the counter or Toyota DOT5.1 should be fine, just use an unopened bottle.

Well, the "old" bottle has been kept indoors and has only been open for a couple of months

Just for info, I fitted brand new UK calipers and braided lines front and rear and chaged the fluid throughout.

I used less than 2 litres of fluid.

I've read somewhere that it's always best to use "fresh" bottles as opened ones absorb humidity hence reducing the boiling point.