If you are going to use any formula at 12 months +, the recommendation is to use toddler or growing up milks. The follow on milks are only for babies 6-12 months. But no, we switched to cow's milk at 12 months. It's cheaper and easier. It's also a whole, natural food, as opposed to a synthetic one. The way I see it is I don't drink nutritional shakes (which is basically what it is) in place of eating healthy food, so I wouldn't feed my kid that either. It's also higher in sugar than cow's milk and many of them are lower in calcium. You should still offer a vitamin drop because kids up to age 5 in the UK are recommended to have vitamin d supplementation (you can't get much vitamin d from food), but I wanted to move in the direction of getting all other nutrients from real food. And again, it's just so much easier and cheaper, and my daughter liked it so much more.
Which? did this great side by side comparison of toddler milk and cow's milk though, which I think is really helpful, showing how they compare nutritionally and by cost.
https://www.which.co.uk/baby-and-ch...the-right-formula-milk/toddler-formula-milk-/