From my research prior to my conversion I discovered that a major problem with mixer systems on an injected engine is the probability of backfires.
On the petrol side the injectors are turned off on overrun (hence the 999 mpg on the MID/CID), this does not happen with the mixer gas, so the inlet manifold will be full of a gas/air mix which is not required. Some of this will be passed through the system into the exhaust, and pssibly back into the inlet via the SAI. Should this ignite due to a hot exhaust/cat then there is a risk of the inlet plenum "blowing up" also through the SAI, with subsequent damage. The fitting of a "pressure relief" valve to allow this "explosion" somewhere to go may prevent the damage.
Now i might have got some of the "understanding" of the problem a bit wrong .. but the gist is, I believe, correct ... mixer on injected = high risk of backfire and damage.
Having said that .. sequential system is brilliant and saving me shedloads of cash ..
