Well, any ring is a good promise ring. As it is all about the meaning while giving the ring, not about the promise ring itself.
So there are no ‘rules’ about good or bad promise rings. You surely can give any ring you like.

That being said, the receiver of the ring will love the fact if you put some serious effort into it. And that you tried to give him or her the prettiest ring available. A promise ring he or she will certainly appreciate.

So you have to keep in mind what that person likes in a ring. A ring with big flashy diamonds, or just a simple golden ring?

Maybe you can ask close friends or family if maybe they know what he or she likes? So you can give the ring as a big surprise.

But other people will like it much more if they can choose the promise ring themselves.

So it all depends on the receiver of the ring and what he or she likes. But there are no good or bad promise rings.