For mathematically sophisticated readers, Meyer is an excellent text on stochastic calculus with applications to finance. It is at a technical level comparable to Oksendal (2003). It differs from that book in that:

Meyer is more focused on the theory of stochastic calculus, and

Meyer provides a far more detailed and up-to-date treatment of financial applications.

If you are looking for a first introduction to stochastic calculus, don't read Meyer unless you have very strong skills in measure-theoretic probability. Any deficiencies that may exist in your mathematics background will soon be revealed by this book. Do you know what bounded variation means? How about an equivalence relationship, or an orthogonal projection of a random variable? This is masters level mathematics, and Meyer assumes you know it.

As a reference or a second book on stochastic calculus, Meyer is outstanding. In a formal, highly rigorous manner, he develops stochastic calculus, all the while focusing on topics of primary interest to financial engineers. He emphasizes multi-dimensional processes to a far greater degree than other books.

Lots of introductions to stochastic calculus illustrate concepts with basic Black-Scholes theory or other classic financial applications. Meyer goes beyond this, delving into modern financial engineering applications. The last third of the book is devoted to this material, culminating with a sophisticated chapter on yield curve modeling.