We have some grinders from Speakeasy Innovations in Santa Cruz CA. They have two innovations that set them apart from other grinders that we've seen:
1) Sharp, knife like serrated teeth. These are designed to cut your herb rather than tear it, which leaves more trichomes on the leaf.
From their website: The PocketTumbler's™ Patent Pending features are designed to fluff by Tumbling, Cutting, Slicing and Serrating. This cutting process creates multiple lengths and textures that allows more air to easily pass through.
2) A loading area (without teeth) for your bud so you can close the grinder before actually grinding.
These two features make this the easiest spinning grinder that we have seen. No more heavy pressure for that first revolution as the bud is mashed into the grinder.