Field boots @ the lower levels are perfectly acceptable. Don't let the DQ's (and I am one) scare you off. Honestly, the judges aren't even going to notice. I still see jumping saddles @ training on occasion.
Of course field boots are acceptable. What TheHorseProblem was telling you is that the vast majority of dressage riders show in dress boots. Now, let's talk about the boots in question. I don't understand the design. They have zippers up the back and the "laces" don't actually tie. What is the point of fake field boots, especially for dressage? If they were the only boots I had, sure, I'd show in them. Would I buy them specifically for showing in the dressage ring? No.
Founding member of the "I Miss bar.ka" clique
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I do have these boots and while I am an eventer at heart I will occasionally show 'real' dressage I love these boots they are super comfy. As someone said above 'fake field boots' the laces are elastic so they are a little more forgiving then normal laces. I love the ease of having a zipper too.
I would say if you like them then go for it!