Is this a recent kitchen installation? Could you ask cabinet maker to adjust the base units across to close the gaps up a bit more? Even if the splashback needs to be re caulked, better than trying to infil with stainless steel angles.

I say don't. My friends looks bad after two months. Stained with white circles from water damage. However , hers doesn't look sealed or oiled well enough. It's quite raw looking. Some woods must be more suited then others. If you don't have children and don't leave anything drying or wet on your benchtops it would be ok.

We have black pearl granite. Been in around 10 years and looks as good as the day it was installed. Easy to clean and doesn't seem to mark or stain. I would however not use black again as I think white would of looked much better. Granite being a natural product can't be matched up as easily down the track if you decide to add more benches and the like. Each batch can potentially be different.

Are you up to DIY? Plenty of examples on Pintrest.