The Red shop rags are made for real Grunge work...I use them on the engine compartment...saves your MF's from getting oil or grease on them if any is present...being as course as they are they act like a lite scrubber...so they get the grease off...also work good on tar removal inside wheel wells....just use them where you need to do grunge work...not on paint...better than using MF's for real dirty jobs...and wash seperately..not with MF's....also good for wiping tools down after working on the car...
Some people are looney and use micros on even their engine, the shop rags are perfect for engine use. My micros will never touch an engine or areas where large dirt particles can get embedded.