This page discusses the types of ravioli makers on the pros and cons of each.
There are two general types of ravioli makers. Those without a bottom and those with a bottom.
These two images show an example of each
Then within each category, the various ravioli makers come in an assortment of sizes and shapes.
Here are a few more examples.
Aluminum Ravioli Form
Round Ravioli Form
Small Ravioli Form
Toasted Ravioli Form
But let us focus on a comparison of the bottomless ravioli maker as compared to one with a bottom.
A form without a bottom has a very significant advantage. With a properly made a pasta dough, which means one with well developed gluten that allows the dough to stretch without ripping, a bottled list form will adjust for any differences in the amount of filling. This adjustment means that the filling does not flow into the sealing area.
If the filling flows into the sealing area, the ravioli will open when it is boiled. And the filling will blow out of the ravioli.
So with the bottomless form you do not have to be as exacting with the amount of filling that you add.
With the form with the bottom, if you add just a little too much filling, the filling flows into the sealing area. To present this you must either under-fill or fill the exact amount to prevent ruined ravioli.
Watch this video to see exactly what happens.