Many have noted and even built businesses around being a secure DNS server provider.
Many issues are addressed, such as making the DNS query secure so third parties, most notably your ISP, cannot see the DNS query.
While it is true that a third party monitoring your connection cannot see the content of the query, they can see when a message is sent to the DNS provider’s IP and which IPs are subsequently used by your computer. This is not as informative, but still contains a bit of information about you.
But then there is the blatant issue. You are hiding your information from some parties, but handing it directly to another, the DNS provider.
Consider well why a business would provide this service, especially when they provide it free.
Data collection has little impact when done on a small scale. When done on a large scale it can be extremely informative and lucrative.
Providing the DNS service for free, offering faster query response, and a secure link is great marketing. But you are handing them all the data about you. Now they have a large data set to work with. Now they know you and those around you well. Now they have data of value.
If they state they can be trusted, is it true? Are you their customer or their product?