That is a cool stool! Ours is from Ikea, and cost $20; it is made of wood and has two steps (the top one is wide like a platform). It puts Nathan at chest height with the counter, so it is perfect for helping and watching.
Sara, one of Nathan's little toddler cutlery sets came with a 'knife' and that is what we use for him to help cut things. It is basically a very blunt butterknife with a good sized handle. It works with playdough, as well, or just goofing around with cookie dough. Let me know if you find anything that works to stop the tasting; I have to keep an eagle eye on Nathan so he doesn't grab handfuls. Not a huge deal when it is cookies (although still not a good idea), but when it is meat it is terrible! We made meatballs together the other day and I eventually just put him down and deal with the tantrum. He wouldn't stop trying to sneak bites.