I did one and have discovered who my grandfathers biological father was. He was born out of wedlock and his mother never disclosed who his father was to anyone and he was raised by his grandparents believing his mother to be his sister for much of his life. Sadly I found out who his father was after my grandfather had passed on.
I've connected with many relatives on there and have got photographs of my great great grandparents which my great aunts and uncles never had, they'd never met them because they both died tragically young. I had the biggest shock when I saw the photos because my great great grandfather looks almost identical to my dad and my brother, at a certain age they could pass for triplets!
I've also tested many family members and downloaded and reuploaded my results into a few other websites, one of which was called Codegen which brings up relevant articles related to illnesses connected to what genes you have. As an example mine brought up many articles about mental health, which I do suffer from. My mums said she has an increased risk for esophageal cancer which is what her father died of, I'm not sure how accurate the results are but ours have been pretty accurate from what we can tell.
You can also upload to Gedmatch where you can match up to other relatives from other DNA testing sites if they have uploaded the results there too. It also has other things, or did when I used it last, like predicting your eye colour based on your DNA (very accurate).
Using mine and my families DNA I was also able to genetically confirm the research I'd already done on my family tree which I was happy about.
I was also pleased to see a small amount of South Asian DNA in my results, I'm part Romany gypsy and often we have trace amounts of South Asian in our DNA but sometimes it's so small it doesn't show. The last couple of generations of my Romany side people have married non Romany people too so mine would be "diluted" more I suppose so I wasn't expecting it to still show up.
If you're interested in your Ancestry then I really recommend it. Although I can't say how it compares with similar DNA testing sites so there may be better ones out there.