I'm sure they've gotten better as time goes on but those tests aren't entirely accurate. With breed populations being different and how traits are inherited and then sequenced and breeds with shared ancestry it can get a bit muddled.
There have been a lot of people sending in known mixes and primary breeds or the breed they behave the most like are not identified.
I think they're a good basis and fun for sure but I'd be reluctant to treat them as a definitive answer.
Embark is the most expensive and most accurate. I had my dogs tested about 10 months apart. There were advancements in those 10 months. Shelby is my GSD mix. Without testing, she is clearly mostly GSD. When I posted her pictures on the board, years ago, the consensus was that she was PB GSD. She wasn't.
Shelby, and her littermates were dumped in a KY shelter. They all looked alike, except 3 were stock coat and 3 were plush. They were all black with tan markings. According to Embark, she is 75% GSD and a small percentage of 2 other breeds. The other 2 breeds are black and tan dogs.
My hound mix, looks mostly beagle. Embark has his mother as PB beagle and his father as a beagle mixed with 3 other breeds.
Embark also tests for about 170 genetic conditions. In the 10 months between testing for my two dogs, Embark is testing for more conditions and can identify more dog breeds. While some conditions may not apply to our breed, DM was an important one for me. Shelby tested not at risk and/or a carrier for DM, as well as being completely clear and/or not at risk for all other conditions that Embark tests for.
My beagle mix only tested as a carrier for wide angle glaucoma, but not at risk. He is negative for all the other, many, eye related conditions beagles are prone to, as well as all the other conditions tested for by Embark.
Embark costs about $200.00, so I wouldn't do it for fun.