Recently I've had some problems with the launcher, where it didn't want to even launch the game, but apart from that, it didn't see that 2.5.1 was available so I couldn't update.
So I did some research into installing MXL Sigma manually, and I've been thinking, that installing manually should be an official secondary download method, if you see what I'm saying. So instead of just being forced to install using the launcher, we should have a directory or so where you can view several sigma version files and be able to choose, download and install manually.
I noticed that a good few people were looking for older versions of Sigma (1.8 and older), but with the launcher system, where it forces you to update and you lose the older versions files, it's a real problem you see.
Of course there is the unofficial way of installing sigma, and also there's that trick with the link to fetch sigma files from the website server, but as far as I checked, this trick doesn't work for anything older than version 2.0.0... I'm sure that not everyone will be doing all these tricks to fetch files and so forth, so I think different versions should be made more available and there should be information in the download page of the website that this is a viable official installation option.