Will this clamp seal a leaking joint on its own, or do I need sealant?

The clamp creates a mechanical seal when tightened properly — most shops don't use additional sealant with band clamps. If you're sealing a split or corroded pipe, prep the area clean and bare metal first, then tighten gradually to avoid over-clamping.

How tight should I make it?

Tighten until the joint seals and stops leaking, then stop. Over-tightening a narrow band clamp can warp the tube. You're aiming for firm contact, not maximum torque — hand-tight plus a quarter turn is a good starting point for most 2.25" joints.

Can I reuse this clamp if I remove it?

Yes. Stainless band clamps are reusable as long as the band itself isn't bent or cracked. If you're doing exhaust work and need to disconnect and reconnect, you can pull it off and re-tighten on reassembly without replacement.