Hiker grommet presses are good presses. They are adjustable for different thickness and you can cut and set in one operation. Punching through 4mm coraplast is very easy.The only drawback that I know of is you have to use hiker grommets. Hope this helps.
We also use a Hiker press and #2 grommets. As Butch said, the press easy to use and it works well. It comes either with or without a plastic base. Out of convenience, we bought the base, which has a tray on each side for storing the top and bottom of the grommets while you are working.
I have one for sale that you might be interested in. I used it for about a month. I was using it to put grommets on towels but the material on the towels was too thick to punch a hole and put the grommet on at the same time. So i would have to punch the hole and then change the die so that i can put on the grommet. We now have our supplier ship the towels with a grommets on them. But overall its a good grommet press. The one i have is a CStep-2 by Clipshop. I have a #5.5 and a #3 hole piercer and grommet die. If you are doing banners you wont need the hole piercer but i can throw them in as well. I also about 400 #5.5 grommets and washers as well that i did not use. Contact me if you are interested. It will sit in the corner forever until i get rid of it. See attachment.