There are two reasons to use a zero-clearance plate around your table saw blade:
- to support the workpiece more completely, for less chip-out and splintering; and
- to cut small pieces that would fall through the larger hole in the standard insert.
This insert requires finicky adjustment for the first point, but serves quite well for the second. In the tradeoff between lower cost and higher performance, this is the lower cost option.
The plate is made of molded plastic with a rectangular grid of supporting ridges on the underside. (It's very similar in construction to the standard insert plate, but made of plastic instead of metal.) Because the plate is soft enough for the saw blade to cut through easily, it isn't impressively stiff. And it's not just a drop-in replacement as the metal plates are; you must fasten it down with four phillips screws. And you can't just tighten these down all the way, either. The plate would normally sit below the level of the saw table. These fastening screws are just outside the height adjustment screws (which use slotted screws, so you'll need two different screwdrivers) and the plate is flexible enough that the combination of screws forms a spline curve rather than a fixed plane as you attempt to adjust both the height screws and the fastening screws.
At first thought you're probably appalled by this idea, but in practice you can make it work acceptably for 90 degree cuts. What I ended up doing was to make a curve that's uniform left to right, and dead even with the tabletop as it crests at the axis of the blade. A wide workpiece will be supported by the table proper, and it doesn't really matter if a narrower workpiece slides up and down a smooth curve as long as it's at exactly the right height as it crosses the blade.
The downside here is that if you're expecting to work with your miter gauge set to anything other than 90 degrees, you're limited to work that's wider than the insert because the plate won't be both flat and at table height. Alternatively you could build up the bottom of the plate with washers under the fastening screws, and something (Bondo?) at the long ends. Or you could just buy a more expensive replacement that's easier to make both flat and level.
Personally, I got this mostly to cut small trim pieces without having to go fish them out of the built-in bucket that collects sawdust under the blade. This insert was cheap and does an OK job for what I need.