DVD Multi was a standard issued a few years ago to give the hardware manufacturers requirements so that equipment would read most DVD formats sanctioned by the DVD Forum. It's not a dvd type or format. Just means Multi drives should be more compatible with a variety of dvd types. Basically -ROM, -R, -RW, -RAM disks. Does not include DVD-RAM cartridges and 8cm disks.
Just looking at specs of Super Multi drives, they seem quite similar to ordinary drives. Some are a bit faster but that's just because they are newer. I've found some that don't do DL so it seems more of a flashy name as far as most people would be concerned.
Never had a problem with my non-Multi drives!
DVD DL refers to a dual layer dvd disk that can hold 8.5Gb of information by having two layers that are burned. I don't know if home burned DL disks are included in the Multi spec. Commercial DL disks are produced by a very different process (such as etching) which is far more reliable to read.
That's all I know.
Starman*