Currently my backup strategy invloves :-

1)I have one master server and two slaves (Data approximately 700 GBs and tables are of mixed innodb and myisam).

2)I take weekly and monthly backup from slave through mysqldump.

3)In case of slave failure ,will copy data from another slave.

My question is should i change this backup strategy ?? Should i use percona xtrabackup and if yes why ??