I don't really have much trouble with them. Put thumb on top, wrap fingers around can, press with thumb and pull. For a small operation, the HDPE holders are pretty attractive, IMHO. There's some free branding, assuming you can pick a color no one else in your market is using. Plus they can be put on the cans with nothing more than a rubber mallet, and they're durable enough that they can generally be reused at least a couple times. As you say, there's also the environmental consideration - for some reason, consumers don't realize that the old-school rings are recyclable.
The only other option I've seen is the plastic rings that go around the center of the cans and have a carrying handle.