There is a list of verified sites on the site: TubeMate YouTube Downloader 2.2.6 - Official Websit
But since it is not on the Play store, you should install it at your own risk, from verified sources or otherwise. It's probably not on the Play store because it violates Youtube's terms of usage in some way.
For security concern check app behavior, control its access and limit other access. Like camera, location etc
Tubemate works fine.
Android has malwares not viruses.
Hi Guest we just wanted to alert you to a major change in the forum. We will no longer be allowing the posting of outgoing links. Please use the attachment feature to attach media to your posts.