Here in the shop we use a Wicked Edge precision sharpening system set at 30 degrees. We are very pleased with the results that we get with this fine machine and highly recommend them. If however you do not want to invest $400-$600 in a sharpener we would recommend any of the systems that use a clamp on the knife and guides for a controlled angle while sharpening. Most of these systems will offer the 30 degree setting.
We use the 30 degree angle because it is a great field edge. The 30 degree angle is sharp enough for any task other than fine surgical style work and it is a very durable edge.
Once a Habilis product has been sharpened several times (6-8 on average), the angle will get steeper. When this occurs the blade needs to be sharpened like a traditional Scandi grind in order to reset the original blade angle dynamics.
Once this is done the knife can have the 30 degree angle put back on and be ready for use.
For field maintenance I recommend the Smiths Pocket Pal, it is small and has both carbide and ceramic sharpening stages and both are set at 30 degrees. This sharpener also has a tapered diamond rod that is good for sharpening fish hooks, gut hooks and serrated blades.The tapered rod also makes a great marlin spike for knot work.
Hope everyone finds this helpful -Steven