AP BBK juddering

[KenM3csl]

Sorry for another brake topic ,

I have the AP setup with DS2500 , my steering is going everywhere when i brake .
Sometimes after a longer easy drive it improves . After a few time hard braking it gets worse .
I know / hope that it' the DS2500 fault , I will purchase RS 29 very soon.
If I look at my disks there are some darker spots , is this the pad residue ?
Is there anyway I can confirm my disks aren't warped ?

Thanks