These are great to have on hand when you're not sure what the weather is going to be like and you want to be prepared for the unexpected chill. They fit quite snug so there is no worry of them sliding down during a ride. I've got real slender legs and I find them to be a little too constricting in the upper legs so bigger guys may find them even more uncomfortable than I do. They actually do a great job of offering insulation and wind protection as I tested them a couple of times in the mid thirties.
These are by no means a substitute for good leggings. Truth be told you are much better off wearing a good pair of leggings as they are cheaper and fit more comfortably. They'll even look better on you because although these warmers appear to be well constructed from quality materials they are quite sheer when worn so during the strong sunlight of a mid-day ride they might look like stockings. Wait for dusk before stepping outside.