[Stoves] You can patent the steak but you can patent the sizzle:

[Richard Stanley]

Crispin, DAn et al, 

On the patent and protect issue,  why do it: The day will come when everything is  open source anyway

--except for one thing: 
The personal stamp of your individual input in the design, the concept/ rationale its evolution and the problems and issues encountered along the way its use and likely prospects ; It may all be irrelevent to someone buying a new drill  but its very inportant to a person who is about to launch a stove or biomass project in a new area.  

Its been said by more than a few marketing gurus that people buy the sizzle, not the steak: As applies to less  glittery and more substantive technical designs such as things stoved and fuels, seems to me that they are buying not only the product but as important (moreso, where it is  relatively unkknown), your credibility and concern, your responsiveness, thoroughness and tact of your interaction with them.  
Sure anyone can run away with all this stuff but no one can duplicate your own personality and perceived handling of an inquiry..
We see all kinds of rip offs and some incredibly brash attempts at swallowing our work whole but you know  what: No one can swallow what we represent in terms of our  response and follow up support for what we sell. That may not be the best way to handle an enquiry but it seems to work for us and what we do. You are all in the  same boat with your own products and services.
There are now about 25 generically different presses for making the wet process briquette, There are likewise about 5 videos showing how to make it as well (some are downright entertaining) .
So why buy our manuals? Well if you do, you have the guarantee of follow on support, the "what to do if you do not have x, or encounter Y, in z situation kind of support" , which is almost impossible to cover in print...

Seems to me that it would be no different with everything you buy from any other person, particularly when they are small guys with  novel products or services.
It gets more interesting when you open up the idea to others to co develop over a wide area--as you can do with the internet. 

pressing on 
Richard Stanley
www.legacyfound.org