I'll be doing the same soon. I have a Dewalt Random Orbit sander I've owned for a while, which I tried on a chopping board which came with our kitchen, which is the same exact wood as the worktop itself. Not saying you should or shouldn't use an orbital and I have read about using linear sanding to go with the grain, however, in my experience of using my orbital, it worked absolutely fine.
I started with about 60 or 80, then did 120 and then finished with I think a 160 or 180. I can't remember what I had on hand at the time. If using Osmo oil, the recommendation is not to sand to too fine a grit, since it will stop sufficient penetration and absorbtion into the wood. So 240 would arguably be too fine.
I was actually quite surprised by how quickly some very harsh chopping marks from knives came right out after only minutes. The same with water/black marking stains to an extent.
In terms of the product to re-finish. I couldn't decide between the raved about Osmo Polyx oil vs the Osmo Top Oil. From a read around online, it seems that the top oil is basically the same stuff, just that they have the certification for food safe on that one so market it mainly as for worktops. It's essentially a similar product to the Polyx oil.
In the end I went with the Polyx as it comes in 3 different (clear) finishes. I ordered sample packs for a few quid each, from Osmo website in the Clear Satin, Clear Matt and Clear Semi Matt. I didn't want to re-finish in anything that would add orange colour back into the wood. We also have a lot of water staining and a lot of water splashing direct onto the sink area so I bought some Osmo 4006 Wood Protector as well. This you give one or two coats before the main Polyx oil, to really help protect from water. This is optional, and is does slightly darken the wood, but it's minimal imo and the wood darkens anyway a tiny bit from the Polyx.
So with the finishes. They are pretty much as you would expect:
Clear Satin = You get quite a noticeable sheen. Personally to me, it looks cheap. When I walk into our kitchen and it's mildly sunny out the back, you get a lot of glare off the worktop with this, and it looks like a cheaper varnish. However, my wife and son said they preferred it to look at up close as it adds a bit more colour and life to the wood.
Clear Matt = It will add a tiny bit of darkness/colour/vibrancy into the wood, but otherwise very natural and the closest to just bare wood as you will get.
Clear Semi-Matt = A middle ground between the two but more towards matt. A very, very slight sheen and a bit more vibrancy in the wood compared to the full matt in the samples I tried.
So I've gone with semi-matt. Haven't started fully yet as trying to work out a good order as decorating the whole kitchen as well anyway.
