This is just a how to for the folks out there with an L version machine.
There are in fact two bios versions for the revo build, a normal version and an L version. This is visible by looking at your bios menu or using a program such as speccy to see motherboard details.
The bios initially provided by Acer on the download page will fail when tried on an L Bios version, stating its not the right version.
To download the correct version for an L bios version go to the acer driver download page as normal for the m1-601, but insteade of looking at just the latest versions, change the search (box RHS just above listing) to all. Another bios will appear, the description is the same, but the key is it has and L in its file name.
When downloaded and expanded you will need to follow the instructions to flash under DOS, by creating your own boot disk (I used RUFUS to create mine). It flashes with no problems at all
Took me a while to figure this out, as Acer has done a great job at hiding the bios listing