Is this glue waterproof?

Yes. Ardell lists it as waterproof, and owners report it holds through sweat and humid weather. Removal still needs an oil-based remover or warm water and soap.

Can I use it with cluster or individual lashes?

It is made for strip lash bands, and the brush works for cluster styles too. For individual lashes, a thinner glue with a finer tip gives more control.

How is it different from the classic DUO tube?

Same clear, waterproof idea, but the brush lets you paint a line instead of squeezing a drop onto a wand. The tube gives a more precise dose; the brush is faster and tidier.

How do I stop the brush from clumping?

Wipe the brush on a clean tissue after each use and close the cap tightly. Store it upright and avoid dipping it into glue that has already started to skin over.

Does it dry clear on dark lashes?

Yes. The adhesive goes on white-ish and dries transparent, so it blends with both black and brown lash bands.

Use an oil-based makeup remover or lash glue remover on a cotton pad, hold it on the lid briefly, then lift the band off. Do not pull the lashes off dry.