Not wanting to advertise Reddit use too much, but you should look at the posts by u/bosseschreibt. He/she/they take some great pictures of writing samples with a number of Document inks, sometime side by side. One of their posts actually made me want a sample of Koh-I-Noor Document Blue. Anyway, their pictures are a great for seeing samples of various Document Inks from multiple brands.
Not wanting to advertise Reddit use too much, but you should look at the posts by u/bosseschreibt. He/she/they take some great pictures of writing samples with a number of Document inks, sometime side by side. One of their posts actually made me want a sample of Koh-I-Noor Document Blue. Anyway, their pictures are a great for seeing samples of various Document Inks from multiple brands.