Also (I agree with all the other posters), just a tip, if you're wanting to grow your horses's mane/tail out, I'd advise against using a silicone based product, like ShowSheen. In the long run, it'll make the hair more brittle and prone to breakage.
My favorite product for tails is Cowboy Magic detangler, along with literally soaking the tail in human conditioner on a monthly basis.
I don't like it so much for forelocks (too oily, weighs down the hair and attracts dirt in that area, that I've found) and it's alright on manes. My favorite for manes and forelocks is pretty much any kind of child's spray in detangler. I love how most of them don't leave a residue and they keep the hair light instead of weighing it down with a bunch of yuck.
Really though, I'm kind of a snob about Lacey's mane, tail, and forelock and there's a 99.9% likelihood that your horse will be just fine with whatever product you choose to use.