Will this fit my existing circline fixture?

Only if the fixture takes a 9-inch circline tube with a G10Q 4-pin base and a ballast rated for a 22W FC8T9 tube. Check the old tube's markings before ordering.

Is it a direct replacement for an older circline tube?

Yes, if the old tube is the same FC8T9/CW type and base. Match wattage and base, since the ballast is built for a specific tube.

Can I use it in a dimmer or a fixture with an electronic ballast?

It is not designed for dimming. It works on ballasts meant for this tube type; a mismatched ballast can cause flicker or short tube life.

How does it compare with an LED circline replacement?

LED circlines use less power and contain no mercury, but many need the ballast bypassed or removed. This tube drops into existing fluorescent setups with no rewiring.

What is the color temperature and what does it look like?

It is 4100K cool white, a neutral-bright tone that suits kitchens and utility rooms more than cozy living spaces.

How should I dispose of it?

Treat it as mercury-containing hazardous waste. Take it to a local household hazardous waste site or a retailer that accepts fluorescent tubes; do not put it in regular trash.