The latest entry level Canon cameras i.e. the 2000D and 4000D will only work with Canon flashes.

Auto focus is easier, but camera will not necessarily be focusing at the optimum point, using  manual focus and setting your magnification factor you can get all your images of every patient the same magnification every appointment, regardless of who takes the picture.

Make life easier for you and your staff to get consistent results in terms of quality, magnification, colour and exposure […]

The ETTL (Evaluative Through The Lens) settings are equivalent to putting your flashes on Auto. Each time you fire your flashes on ETTL you might have a different amount of light being thrown on your subject.