InstantCheckmate.com is not run by government agency, so there is no guarantee that it has correct or complete information. The company compiles arrest and conviction records from multiple government sources, so it might provide helpful information or leads as part of background search.
Instant Checkmate does not publish the list of databases they compile and use to perform background searches. In addition, a search on the website requires the user to input personal information about the person they are researching; if the user inputs the wrong name or personal information, the search might not find existing records. Instant Checkmate states on their website that they do not guarantee the accuracy of the information they report, but their website compiles at least some records from each state.