Hiker, Fasnap and Stimpson seem to be the leading makers of manual grommet presses. If I'm not mistaken, all the grommets are proprietary for each manufacturer so having a good supplier of grommets is a first consideration. Fasnap and Stimpson may be interchangeable, I'm not sure. All three are good and will do the job, compare the cost of the presses, the continuing cost and availability of the grommets and pick any one.
If you are looking for more than a manual press then Edward Segal is the leader.
If you are looking for more than a manual press then Edward Segal is the leader.