Is the 28.6 Ah battery rating real?

Treat it with suspicion. A handheld saw battery of that capacity would be enormous and heavy. Expect a small pack with minutes, not hours, of cutting per charge.

What can a 6-inch cordless chainsaw cut?

Branches, saplings, small logs and brush up to roughly the bar length. It will struggle with hardwood trunks or anything much thicker than the bar.

Does it come with a charger?

Most bundles include two batteries and a charger, but check the box contents for your listing. Batteries are brand-specific, so spares are hard to source later.

How does it compare with a Worx or Sun Joe mini saw?

Those brands have better parts support and more consistent runtime. The Gped competes on being a low-cost bundle with two batteries.

Is it safe for beginners?

It is small, but it is still a saw with an exposed chain. Wear gloves and eye protection, keep both hands clear of the cut line and never cut overhead with one hand.