Steel plate is only effective for particular oven owners with particular goals. Since the metal transfers heat faster than ceramic, it speeds up the bottom bake. In order to brown the top/melt the cheese before the bottom of the pizza burns, a broiler has to be used. In other words, in order to see what steel is capable of, you've got to have a broiler in the main compartment and be willing to use it (Dmc isn't).
Beyond requiring a broiler in the main compartment, in order to hit the bake times that most people purchase steel to achieve, you need an oven that goes to at least 525. Many ovens that have 500 as the peak temp on the dial run a bit hot, so, for these owners, there's hope, but you'll want to measure how hot your oven actually gets before investing in steel.
Steel is for people looking for a specific style of pizza- chewy, puffy, lightly charred NY style pizza that's baked for about 4 minutes. The fast bake provides better oven spring for a puffier crust, but, you generally don't get a lot of crispiness. If you prefer a crispier NY slice, then steel is no better than a typical cordierite baking stone.
If you are going to invest in steel, unless you have an oven that exceeds 575, you generally want at least 1/2" thick steel. Not only does 1/2" steel guarantee the magical 4 minute bake at 525, but you can make more pizzas in one sitting without depleting it's heat.
Another factor to consider when purchasing steel is length and depth. On NY style pizza, in order to prevent boilovers, the rim generally has to stay the same width, regardless of diameter, so when you get into smaller pies, they tend to be all rim with very little sauce and cheese. When launching, it's far easier to have a target that's bigger than your pizza. In order to comfortably launch pies on a 14" plate, you'll want to make pizzas in the 13" realm- and 13", for NY is WAY too small.
Great pizza is about balance. The sauce and cheese area should complement the rim. If you're buying a plate that limits you to 13" pizza, you'll be serving your guests mostly bread. When sizing steel plate, you want a square as large as your oven will accommodate- touching the back wall (or the back of the shelf, if there's a bar) and almost touching the door, with about 1" gaps on the sides for air flow.
You also, when purchasing steel, will want to purchase it locally. Out of the couple hundred members who have purchased steel locally, no one's spent more than about $60, with many spending considerably less.
Summing up. Steel is the best hearth material you can buy (for people with particular goals and particular ovens). This particular product, though, is an overpriced, poorly sized, complete waste of money.