That article doesn’t cover it all, indeed.

There are many cases in which both can be used, usually “bon” is more dated and formal than “bien” in that case (only when you can use both!).

Here it means different things, but all four are correct.

On a different topic, casually you’ll often use “c’est” instead of “il est” here, but it’s still correct.

Il est bon de manger des légumes

It is wise to eat vegetables. If you say “c’est bon” here it means “it tastes good to eat vegetables”

Il est bien de manger des légumes

Here it means that same with “c’est“. It means it’s a good thing, it’s very close to the other but there’s a slight difference in tone.

Il est bon de vous rencontrer

It feels good to meet you, it’s a nice experience.

Il est bien de vous rencontrer

It’s a good thing (for my career or the project) the meet you. I wouldn’t use this one.

Another thing, if you see old friends or family you hadn’t see in a while, you might want to say “It’s good to see you”. You could say :

Qu’il est bon de vous voir

If you’re Gandalf. Now we would say something like :

Ça fait du bien de vous voir

Note that there are a lot of missing cases in your article, it’s not as simple as they say it is. For instance, “un bon” is indeed a voucher but “une bonne” is a maid/servant.

Il est bien de sound very strange to me in both case and in general. So I would go with il est bon de in both case.

However, il est bon de is very uncommon. The only sentence I can remember with il est bon is a song based on a Bible translation from the 1870s…

You would use C'est bon/C'est bien in modern French. In this regard, the subtle difference is that c'est bon means it is good to somebody or for something specific, while c'est bien is good in a more general sens. For example, you would say

C’est bien de trier les déchets

because sorting your wastes is inherently a good thing and this is what you want to stress. However, you would say

C’est bon pour la planète de trier les déchets

if you want to stress that it is good for a specific object, here planet earth.

So to answer your question:

C’est bon de manger des légumes régulièrement

Means that it is good to you, for your health.

C’est bien de manger des légumes régulièrement

Means that it is good in general, for example because it is more ecological than meat, etc…

C’est bon de vous avoir rencontré

Means that you fell good meeting this person. You would say this, for example, if you felt down, met someone and that person cheered you up.

C’est bien de vous avoir rencontré

Means it is a good thing beyond the scope of you two. For example, your meeting will lead to a promising collaboration on a important projects.