I have 2 horse slant stock/combo, plan to retrofit with plexiglass for rainy/cold weather. In the meantime, we blanket for cold weather travel and Murphy's law does dictate that you will only have to haul sick horses in cold weather.
I'm very happy with it; it's more flexible for multiple uses than the box horse trailer that I used to have. It's also true that you can put the horse in the front slant stall, so the breeze from the open stock windows is less so they get less chilled.
Look for rubber torsion suspension, for a smoother ride for your horse; and check out the seam between the tack area and the stall area of the trailer - some combo trailers have a gap that allows shavings and road dust (and you know what else) to get into the tack area.