For me, SampleTank 4 has been a great, simple and low risk way to incorporate many more sounds into my live rig.
I am using ST4 very much as a rack synth. That is, as a multitimbral instrument that provides additional sounds to my hardware keyboards.
The synth workstation-like interface, makes it very easy to set up sounds, combine them in all kinds of splits and layers and switch between them using MIDI program changes from my keyboards.
ST4 can run as a stand alone application, so there is no need for a VSTi host, which makes it even easier to run.
I have also bought Syntronik by IK Multimedia, as these sounds can be loaded and played in ST4. Very powerful and flexible stuff.
As for the sounds, highlights include strings, pianos, EP’s, organs, wood winds, vocals and synths. There is a lot of great sounds to discover here.
ST4 has been quite stable for me.
Crashes are rare, but can occur when switching too quickly between instruments based on large samples.
Performance is generally good, but combining large sample instruments can cause trouble.
For an all-round multitimbral software instrument, I think SampleTank 4 is a great choice .