Will this seat lock in place or does it roll freely?

The seat rolls freely on all four wheels with a swivel base. If you need it stationary during heavy work, position it against a solid surface or wheel to block it.

Can I use this on uneven or outdoor surfaces?

It's built for flat shop floors and concrete. Gravel, asphalt, or heavily sloped terrain will make rolling difficult and the seat unstable—stick to level ground indoors.

What's the seat height when I'm sitting down?

Exact measurements aren't specified in the product data, but the low-profile design is engineered for undercarriage and engine work. Test the height before committing if you're between sizes.