One con to consider with genetic testing is that it's possible that not all variations that raise a person's risk of contracting a disease or condition are known.
For example according to the NIH article "Direct-to-consumer genetic testing – advantages and pitfalls", “DTC genetic testing often does not provide conclusive results on whether the consumer will develop a disease or not. Most genetic tests performed by DTC companies are limited to few major genetic variants related to the phenotype of interest, which leads to poor discriminatory power.”