It is true that in most EPA testing, catalytic stoves are about 10% more efficient than the non cat stoves, but this does not necessarily give an entirely accurate picture. The EPA emissions tests and efficiency listings are based on the average of several different test burns at low, medium, and high. Also, a special crib of wood is used: 2"x4" wood for small stoves; mixed "2X4" and 4"x4" for larger stoves; and all 4"x4" for the largest stoves. This is done for consistency in burning between the different stoves. If you always burn the stove on a very high burn the difference in efficiency between catalytic and non catalytic stoves will be less than 10%. If you usually burn the stove on medium or low the difference will be more than 10%.
At high burns the catalytic stoves and non cat stoves are relatively close in efficiency, but as they are burnt at lower and lower rates the catalytic stoves performance improves. At a very low burn the catalytic stoves are much more than 10% more efficient, and at high burns they are close to the same efficiency. The overall efficiency difference is based on the average of the test burns, and is usually about 10%. On the very high burns most of the volatile material is burnt in the primary combustion chamber so there is not much for the catalyst to burn. Also because we have higher flow rates through the catalyst at the high burn it is less effective.
At the other extreme, during the low burn we do not have sufficient temperature to burn the gasses in the primary and secondary combustion chambers in the non cat stoves -- a lot of the potential heat of the wood goes up the chimney as unburned hydrocarbons in non cat stoves. In the pre EPA stoves it was possible for half of the heat of the wood to go up the chimney as unburned hydrocarbons. This means if you did not let any of the heat go up the chimney, by venting the stove directly into the house ( of course you would damage the house and kill any body who chose to stay in the house ) the stove would still only be 50% efficient. In this case, 50% of the heat value of the wood is never released as heat, but is discharged as unburned hydrocarbons -- this is creosote if condensed in the chimney, or pollution if condensed in the air after leaving the chimney.
For years many people have criticized catalytic stoves saying such thing as: They must be burnt hot to keep the catalyst active. This is entirely false. It is true that a catalyst does not become active (lit off) until it reached 400f to 450f. However, in a properly designed stove it is almost impossible to build a fire without this condition occurring. After the catalyst is lit off (reaches a temperature of around 450f) it can burn room temperature smoke if there is a sufficient amount of smoke and 02. The catalyst temperature remains over 450, even if the fire box temperature drops very low because it is creating its own heat by burning the unburned gasses in the catalyst. It will continue to operate as long as the smoldering wood continues to smoke and there is sufficient 02 to burn all the hydrocarbons.
In summery, if your primary use for a stove is aesthetic, and you do not plan to keep the fire going over night, you will probably want a smaller not catalytic stove. If you want the stove as primary or supplemental heat, and plan to keep the fire burning for days or weeks on end, you will probably be happier with a large catalytic stove.
It is true that a catalyst must be replaced about every six years depending on how many hours the stove is burnt each year. Replacement catalyst are between $50.00 and $200.00 Also all catalytic manufacturer offer a 6 year pro rated warranty. So in the worst case it may cost you about $35.00 per year more to operate a catalytic stove. The increased efficiency will more than offset this cost if the stove is used for heating. Maintenance involves taking the catalyst out in the spring of the year, vacuuming the cells with a vacuum cleaner, (NEVER AN AIR HOSE) and storing it in a dry place until the next year. In the Sierra stoves, the catalyst can be easily removed by removing two or 4 nuts. It is about a 5 minute operation. The catalyst I am now using was purchased in March of 1987 and it is still fully operational. The catalyst will work equally on any wood, green, aged, or rotten. The only caution is never burn painted or treated wood in a stove with a catalyst. The chemicals in treated wood (Arsenic) or the chemicals in paint will damage the catalyst. Also if the stove you are using can burn coal, the catalyst should be removed before burning coal -- the sulfur in coal will coat the catalyst and shorten its life.