Its a super simple pedal to operate, just 3 knobs; "drive", "tone", and "level" so its pretty self explanatory. Having a single tone knob rather than seperate "high" and "low" makes it easier to achieve a more "transparent" sound from the TS9 since you can just park it right at 12 o'clock.
In itself, the TS9 only makes one sound, but is good at it. Its not a super hi gain distortion, but will give you a stinging lead tone for soloing and plenty of balanced, sweet sustain depending on what guitar you are using. I play most an Ibanez Ghostrider which is built like a Les Paul with mahogany body / maple top and set neck.
Its not a thick, beefy overdrive, but its not thin or buzzy. Its sort of a sweet, middle of the road, mild distorion, or even just a gentle overdrive if you dial it in low. Its fairly versatile in its range, but its character remains the same through its spectrum from mild overdrive from medium to hi gain distortion.
One thing I like to do with my TS9 is use it as a boost to push a tube amp like my small Epiphone Valve Special into greater breakup.
I also get really cool results by purposely dialing in distorted sounds from the TS9 and then backing off the volume on my guitar to clean it up, like going from the solos in "Black Magic Woman" to the verses which are obviously cleaner, or just to get a clean sound with more sustain than usual.
I've been using mine off and on for a few years now. The thing I like the least is having to always unplug it so it doesn't kill the battery or keep sucking power through the AC adaptor. I do dig how it has true bypass, so it doesn't color my tone when turned of like other pedals do, sort of like rolling the tone knob back a notch or two.
I've never tried any of the other models of TS9's, but I know that I like it better than the TS 808 because it will take you into high gain, and is a bit more modern sounding.
For the money, I would still get this. I wouldn't be satisfied with the cheaper soundtank models, and couldnt get the same vibe from anything by Boss or DOD. And I've never had any issues with it, so if I lost mine, I would definitely buy another one.