I've used it, in several versions, for over a year. It's safe. There has been extensive discussion on at least three forums concerning past history, including Wilders, Spywarewarrior, and SpywareTerminator forums.
Personally I'd recommend the smaller download without the toolbar/WSG, because I don't like toolbars, beyond the basic essentials. (Windows taskbars, browser settings, that sort of thing.)
The current version has had many problems reported with the Clam AV integration...I've had that in the past but don't use it now.
I do believe its realtime protection feature is a big step up from WindowsDefender, and the optional HIPS component is a useful layer of security. (Currently I have that disabled because I'm trying out the "Defense+ in Comodo version 3 firewall.)
I've found some of the toolkit items included in ST quite useful, for example the "analyze file" feature, and the abiility to create restore points. These can be found in other programs, however.
The scan speed is extremely fast, fast doesn't necessarily mean better, though, however since I've had it installed, none of my other scanners, which include the excellent offerings posted by Andavari, have found a thing.
A full scan takes about the "normal" amount of time.
If you go to any of the forums I've listed and search for the program, you'll probably get quite a good idea of its safety.
PS, Andavari, ST uses IE settings for updates etc. Maybe that's the reason you couldn't update?