lean burn will make the engine run very hot and will burn out valve seats - the knock that you hear in lean condition is also called "death" because the valve poppets can become so hot they will start to glow - in which case the ignition timing can go on holiday - because the engine will self destruct - happens a lot of times everyday, engine runs lean, overheats, breaks a valve, valve lands in the cylinder - bam bam - engine becomes scrap.
It has been proven on paper and in reality that anything above stoich ratio will render the engine life cut in a quarter, so back to the original question - WHY should anyone want to invest in such a unit - regardless of the fact that it works or not.
Lets get the tables straight here.
Firstly you NEVER give any ECU screen grabs so people like us can see in plain sight whats going on, You are actually intercepting the AFR or O2 signal along with the MAF and MAP to indicate rich running - hence the ECU cuts down fuel. This is crazy. You are then saying it improves cat life, fuel economy and all that jazz. You are not taking into account that air is going to be sucked into the engine regardless - if its a 1600cc engine with 85% efficiency in pumping it will suck about 1400cc air, by you not providing it fuel wont magically make it an economical engine - it will make it a disaster.
Everything should be explainable in basic terms - so lets go real basic. - datsun A12 engine
if I lean down the carburettor by using smaller jets for primary and secondary throats, smaller idle jet - lean out the idle mix and set the timing a bit retarded - do you know what will happen in about 500 kms of testing? The valves will burn up, the engine will run overheated all the time and will make immense bogging sounds as air is sucked but there is no fuel to use it up.
btw the testing Im talking about is not driving with 5% throttle around a koocha. Im talking about driving it normally with varying throttle from half to full.
I think you are trying to make a 2.0 litre engine use fuel like a 1.0 litre engine - it wont happen, I would suggest you look up a "miller cycle" engine - that engine has separate claims for displacement and actual volumes, mazda actually sold a 929 model with that engine - and I had the chance to see it in Pakistan (our customs did not have a clue on what to apply duty on - because they were born without brains), that engine uses a supercharger to force air back into the cylinders as the valve timing makes it a low pumping loss engine (hence miller cycle). The fuel ratio still remains at stoich in that condition too.
makes you wonder why is there a universal understanding to have stoich A/F ratio