MBM5 is *great* and uses a helluva lot LESS system resources than MBM4. i.e. a typical 6 hour Win2K session with MBM5 updating the tray every 10 seconds has the MBM5.EXE process only having used 15 seconds of CPU time by the time I shutdown.
With MBM4, that figure might be around 45 seconds. So a threefold reduction in system resource usage in MBM5. I'd like to see those idiots at VIA come up with something better.
With regards to benchmarking, the impact is minimal, on the order of 1-3%, much less than any anti-virus program. Of course you should still disable it for accurate benchmark results, but I'm saying the impact on your work is minimal.
Combine MBM5 with ShutDownNow (SHDN) and the benefits far outweigh the undetectable performance hit. If I had one of those hot TBird's putting out 70watts of thermal energy, MBM would be a lifesaver if my heatsink fan ever died. With my cool P3 it's not much of an issue, but still...