The phrase "a very useful source" is correct and usable in written English.
You can use it when referring to a resource or reference that provides valuable information or insights.
Example: "The research paper I found is a very useful source for my thesis on climate change."
Alternatives: "an extremely helpful resource" or "a highly valuable reference."
Anyone who thinks seriously about science, and about how it is used, will find it a very useful source of new ways to appreciate both problems and solutions.
Goodman protested that Mulcaire, referred to in the email as "Matey", was a very useful source for royal stories.
However, the observations have shown that the Internet is nevertheless a very useful source of information for disabled travellers.
Nowadays, the World Wide Web is a very useful source of information for second language students, as they can obtain information about very specific topics and practise a second language.
If you want to know which MP has a valuable voice, which foreign government provides the best free trips, and who got a candelabra for his wedding, then the Register of Members' Interests published yesterday by the Stationery Office, price £1.50, should prove a very useful source.
On the other hand, hay pellets and cubes can be soaked until they break apart into a pulp or thick slurry, and in this state are a very useful source of food for horses with tooth problems such as dental disease, tooth loss due to age, or structural anomalies.
This breadth makes the book a very useful reference source.
"Very useful source of information about what to do with a patient".
This makes Moopz a very useful news source, like Twitturly has proven to be.
A very useful general source that covers some of the issues surrounding OB-RM well, along with many others, is van der Torre 1997.
In the present study we analyzed the proteome of plasma, a very useful clinical source for proteomic analysis in various pathologies.
