Both of those breeds are guarding/livestock dogs so he could very well be appropriate for what you have in mind. Seeing as though the current owners don't like him and even consider him so disposable as to kill him, he probably hasn't received very much (or very good) training. I am a huge dog enthusiast (and trainer) so my first reaction is to urge you to take him (lest he be put down) but you
should be aware that he could have some baggage and issues that would need to be dealt with before he could become a good companion.
The breeds generally make sweet working dogs but without knowing what if any socialization he had (and whether it was positive) it would be hard to say how he'll be. Have you met the dog?
Is it an option to take him and take him to a no kill
shelter if he isn't suitable? Let me know if you need any advice regarding any problem behaviours or anything if you do take him!
Cheers,
Radka and her two border collie mixes