Used one for a few years and I loved it:

• it's precise, you can really aim small UI elements
• It is paired with actual buttons, index on the nub and thumb on the buttons, so no weird gestures to right click
• It is very quick to switch from keyboard to mouse, your hands nearly don't move

But, there's no mouse wheel or scroll gesture and maintaining pressure on the nub is maybe more tiring than a trackpad.

Some people prefer it over trackpad, or use both. Personally I like to disable trackpad because I tend to always hit it with palm or thumb by accident

I use a mechanical keyboard with one on my desktop, I actually use it quite a lot.

I think it works fantastically well. I personally like it much better than a touchpad. It lets me move the pointer without taking my hands away from typing home position.

It’s fine. Takes some time to get used to. Some people really love it, but I don’t think it’s that great.

It's not just for decoration. You can use it as a legitimate pointing device. Nudging it will move the mouse cursor and tapping it with your fingernail is clicking.

It takes some getting used to but you can definitely use it for normal office tasks if you wanted to. That being said, I still personally prefer a mouse. But I have known some people who like using the nipple.

It feels a lot like using a game controller to control your mouse, if you've ever used Joy2Key or similar programs.

Dunno. I have one on my semifake E580 and I just used it to check if it works. It's a bit awkward for me.

Oh yeah.

It isn't a dealbreaker for me, but it really is nice. It takes getting used to, but it cuts down on the need to move to the touchpad or mouse. If you're working in tight quarters, or have mobility issues, or hand issues, it can end up being a major improvement. It's a ymmv thing of course, but I end up using it more than I thought I would when writing.