Is the Hotree 21V good for a full lawn?

No. Its 21V motor and narrow cut suit touch-up work, not mowing a whole yard. For regular lawn trimming, a 40V or higher trimmer with a 12-inch-plus cut is a better fit.

Does it really run on a battery if it lists a 2-cycle engine?

The product is sold as cordless 21V, but the specs also list a 2-cycle engine. Confirm with the seller which version you are getting before buying.

How wide does it cut?

The listing gives a 1-inch cutting width, which is very narrow. Most cordless string trimmers cut 12 to 16 inches per pass.

Can it handle brush and thick weeds?

It is marketed as a brush cutter, but owners report weak power in heavy growth. Treat it as a light-duty trimmer and edger.

What comes in the box?

The listing does not clearly state whether a battery and charger are included. Check the box contents before ordering.

Is it worth it compared with a bigger brand trimmer?

Given the low owner rating and narrow cut, a 40V trimmer from a major brand is the safer choice for most yards. Buy this only for very light trimming where weight matters most.