What's so bad about VCM?
While VCM is a great idea in theory, in practice it has some issues.
During VCM operation, the valves on the disabled cylinders are closed off while the piston continues to move up and down. This creates a vacuum effect in the cylinder, allowing some oil to get sucked past the piston rings into the combustion chamber. This oil continues to collect in the combustion chamber until VCM disengages, at which point the cylinder must burn off the oil before resuming normal operation. This is one way that VCM can cause burning oil.
When VCM is used repeatedly for long periods of time, it can also cause the piston rings to get gummed up with buildup, preventing a good seal and allowing oil to get past the rings into the combustion chamber even when VCM is not operating. This is another way that VCM can cause burning oil.
This oil burning can cause oil fouling of the spark plugs, leading to misfires. The oil burning combined with the misfires will destroy your catalytic converters (not cheap to replace!) over time.
Besides these engine problems, VCM operation also puts stress on the active control engine mounts, causing them to wear out fast. These engine mounts are not cheap. One mount alone (just the part, no labor included) can cost
Simply put, VCM is gambling on your engine for a gain of 1-2 MPG at best. Gas is cheaper than an engine, especially given the very slight MPG difference.