I only have the free version of ST, but do have almost all the other synths. ST is pretty good when you layer the sounds and add some (included) fx. The sounds just need a little "massaging" to sit well in a track bed. The sounds are old, but are very use-able for rock, jazz, blues, funk, hip-hop, techno etc....
Hope your eyesight is really good as the gui has really tiny text, but the good thing is all the synth libraries for Miroslav, Sonik Synth, Sample Moog, Sample Tron etc...can be loaded into Sample Tank.
Of course, we're all waiting for Sample Tank 3 as the current version hasn't had any updates (I think) since 2010, but it's supposed to be released this year???
Best is to try out the free version of ST and see if it's worth getting the full version.