I understand that "silver-tongued" or "silver-tongued devil" means to be a good orator, or: able to speak in a way that makes other people do or believe what you want them to do or believe Merriam Webster.

Is silver-tongued a compliment?

If you are silver-tongued, you are good at persuading people to do things.

What is a Silvertongue?

A "silver tongue" implies one with a tendency to be eloquent and persuasive in speaking.