DNA testing kits are all accurate.
All big companies (23andMe, MyHeritage, FamilyTreeDNA, AncestryDNA) have the same level of accuracy, the difference consisting in the way they analyze and report the deep ancestry.
Genetic genealogy is very helpful when trying to find your kin. Some of these tests can help you find people with similar results, telling you where people that have a similar DNA can be found.
There are more ways of interpreting or understanding genes.
These tests can’t determine if you are prone to different diseases or predict your personality, as these things are mostly affected by outside factors (lifestyle, personal experience, eating habbits, exercising, enviroment).
Even if one test predicts that you are prone to a certain hereditary disease, it is possible to never develop it.