The press that I purchased was the Standard Grommet Tool available from www.grommetworld.com. The box indicated that it is made by Rowley. In addition to the press, I also had to purchase one set of cutting dies and one set of setting dies (I purchased dies for the #0 sized grommets, which are the equivalent of 1/4" grommets). The cutting dies are used to cut the hole in the fabric and the setting dies are used to press the grommet into place.
The grommet press runs about $90 and the dies run about $26 per set. This is a pretty hefty investment, so for casual hammock makers, you are probably better off using Dritz grommet/eyelet pliers (a tutorial for using the pliers can be found in our Tutorials for Common Rat Hammocks and Accessories PDF) or the mallet method.
The grommet press does present some advantages over the other methods, however.
First, grommets purchased from a site like Grommetworld are much cheaper than Dritz grommets/eyelets purchased from JoAnns, and these grommets cannot be used with the Dritz pliers. A package of 15 from JoAnn's runs about $3.75, which comes to about 25 cents per eyelet/grommet. But I have found the packages to be inconsistent, often giving you more washer pieces than grommet pieces, with a total less than the promised 15. Grommets from Grommetworld come in packages of 144 for $7.74 (a little more for black), which is about 5 cents per grommet. Thus, if you make many hammocks over time, that price difference begins to add up quickly.
Second, the grommets from Grommetworld are much stronger and more durable than the grommets from Dritz. You can feel the difference in the weight of the grommets.
Third, a press will set the grommets properly every time. With the pliers, I would occasionally misalign the grommet, resulting in a bent, misshapen, or ruined grommet. The press does not have this problem. If I didn't press the grommet closed tightly enough, I can repeat the press and tighten it without damaging the grommet.
There are a few drawbacks to using a press, however. Obviously, the upfront investment is one. Second, you will need a strong table or workspace to operate the press. It is best if you can screw the press to the table for support, but I cannot do this. The press is heavy and unwieldy and not very portable, so you probably will only be setting grommets in your work area and not in front of your TV or at a friend's house. There is a learning curve that goes along with learning to use it and I had trouble getting the cutting dies to work initially.
However, for professional quality grommets, you can't beat a press.
These pictures do not do the grommets justice - for whatever reason, the lighting was bad and these come out looking rough. The real things are much more polished than they appear in the photo.
Because some things are easier seen in video, I created the following demonstration of setting grommets in a hammock using this press. I will never be a YouTube star, so forgive my clumsy performance. I tried to stay out of the way of the camera - but it was difficult to operate the press and position myself so that I wasn't blocking the view, so it was a bit awkward. However, you should get the general idea of how the press operates and whether or not it might be for you.