For many years Hexamine stoves such as the Esbit have been used by the British army. Each 24hr "Ratpack" would have a folding stove and a supply of fuel tablets. In fact they may still be in use, I've not checked recently. They are also popular with many lightweight hikers. Fuel tablets are one of the most compact and neatest ways to carry fuel, but on the downside Esbit cookers aren't very efficient. Reviewers who have tested hexamine stoves have often been quite shocked at just how less effective they are when compared to other designs. British soldiers have often complained about the mess the tablets leave on the bottom of their mess tins. There are several ways to create more efficient hexamine cookers. One such example is found here and another here. The latter has the advantage that it can also be adapted to other fuel types. Adding any of the windshields described on the Wings pages will also help. This page also has a couple of alternate ideas. The first is a simple way of improving the Esbit cooker itself.
Take an aluminum drinks or beer can. Cut off each end, then cut the resulting tube down one side to create a sheet of aluminum. You'll need this in a moment. Dig out your Esbit cooker. You'll notice that you can have the hinged parts in three positions folded, fully open and half open. Open these fully so the cooker looks like a little bed. Take the aluminum and cut a rectangle. If we continue the bed analogy the length of the rectangle should be a fraction shorter than the bed length and the width twice the distance from the "frame" to the "headboard" top. Fold this rectangle lengthwise and you have a windshield that will close off one side of the cooker. You can make another one of these, but I have a variation of this method. Change the Esbit to the half-open configuration. This is used when cooking with a canteen cup. Now cut pieces of Aluminum to form windshields for both sides. You now have one long and two shorter folded bits of aluminum. Open up your cooker again. You can close off one side of the cooker with the long strip and close off the other by overlapping the two shorter. You've created a cooker with a better contained heat source which means less wind effects and better heat application.
The Hexamine Brew Box.
The second cooker I can claim no credit for. I saw the design in a magazine called "SWAT". I don't have the issue handy at the moment, but full credit for the invention of this goes to the author of that original article, even though I can't recall his name at present.
The Method. Take a sheet of metal, 300x330mm. 80mm in from each end of each of the shorter sides make a 80mm cut. You may wish to trim the ends of the squares created by 10-12mm (shaded areas, above). Now apply a bit of muscle and bend the sheet into a box, 190x140x80mm. You may want to add a couple of bolts or rivets. Along the bottom of both of the longest sides drill a row of eight 15mm holes. The dimensions and number of these is quite important if the fuel is going to get enough air. Take another piece of metal, 100 x 60mm and bend it into a broad U shape, 60mm square and 20mm high. Fit a smaller drill bit and drill about a half dozen holes in the top. This piece is your "Hearth". The final parts needed can be made from wire or strips of metal, bent to have a hook at each end and the correct length to fit widthwise across the box. These are your pot supports.
Using the Hexy Brew Box.
Put the hearth in the centre of the box and place a fuel tablet on it. The inventor of the Brew Box suggests using Optimus Burning paste to help get it going. Place the two pot supports across the top of the box and rest your mess tin across them. You can use a canteen cup on this cooker by moving the pot supports in. When not in use, the mess tins will fit inside the box, and the pot supports and hearth will fit inside the mess tins along with fuel, a tube of burner paste, tea bags etc.
For a constant burning flame when using Hexamine break up the blocks and feed bits in gradually.
A black mess on the bottom of your pans is due to too much fuel at a time.
Soot on the bottom of a pan caused by any fuel will be easier to clean off if you rub the bottom of the pan with washing up liquid before you start cooking. Washing up liquid rubbed neat into soot will usually shift it.
Hexamine fumes are very toxic. Hexamine stoves should not be used in confined spaces.
Mess tins (or any pan) cook more effectively when fitted with a lid. Not only does this save fuel and water, it also keeps dirt and insects out your stew (yes, I know, more protein!). Lids for mess tins are sold, or you can improvise with a piece of aluminum foil. A flattened out pie dish is a bit more sturdy.