This is one of the first firmwares released ever. Some people say that it is even engineering firmware. It is very unstable (much glitches and bugs), but it have two major features that are missing in future releases: edge and IM (instant messanger)! Additionally there is function "Scan" that will allow you to "preview" the songs in your media finder (it will play first song 10 seconds and then move to next song).
Regarding mobile-review.com that firmware is supposed to read TXT files, but we found it do not
There are two files that you have to flash one after another - gsm_sumatra_flash.sbf and gsm_sumatra_mbm_flash.sbf