Hi Robert,
The single most obvious difference between MS and VEMS is the fact that we have wideband controller hardware, whys that better than an external one is the next question - well we monitor the signal from the sensor, and if we loose confidence in its reading (if a misfire has caused unburnt fuel to contaminate the nernst sensor) we stop using the Lambda correction until it returns to an acceptable reading.
Add to that the fact we're using modern surface mounted components, automotive grade connectors in a water resistant box, have had direct ignition control since v3 and our stuff works without needing to do any DIY modifications.
Also when you buy from VEMS you're buying from a single European company that produces and sells the system it has designed, its not buying a kit from the US that has been imported and assembled by by a UK company.
The ultimate advantage is you get to come on here as get your questions answered, oh and we're better looking