Telerik OpenAccess ORM is a much more mature product than LINQ-To-SQL. As a matter of fact Microsoft have stopped developing the DBML format a couple of years back. Our product has been available for over 8 years and its runtime is pretty stable.
A couple of features worth mentioning are our Code Only mapping approach, Round-tripping designer (being actually able to generate and migrate database schema definitions), SDK full of comprehensive examples that show how OpenAccess can be used with different technologies, Data Services Wizard that can create out-of-the-box very comprehensive WCF services for you.
Do have a look at our product page for more information and please let us know if you have further questions.
All the best,
the Telerik team