Can you tell me, are lingual (invisible) braces better than metal braces?

Not usually: Lingual braces are also metal. Because the orthodontist has to work on a smaller arc, the lever arm of wire length between teeth is shorter, and therefore less efficient. Lingual braces can take 25-40% longer than traditional braces (which are also available clear), and often some outside treatment is necessary for finishing. The most efficient orthodontic appliance is traditional braces.

No: first, they are metal, second, most people have terrible experiences with them as the brackets, placed lingually, can cause significant irritation to your tongue, 3rd they are typically less effective. Those are all reasons why we won't even provide them. I would look into clear brackets or invisalign to obtain the invisible results you want far more effectively and less painfully.