How does this AT-AT compare with the UCS AT-AT?

This is a much smaller set at 525 pieces. The Ultimate Collector Series AT-AT is a large, highly detailed model with an interior; this one is a compact brick-built version for display.

It is a Star Wars vehicle build aimed at older kids and teens. The piece count is moderate, so it is a reasonable step up from small sets, though the walker is more of a display piece than a play set.

Does it come with minifigures?

The set is described only as a 525-piece AT-AT build. No minifigures are listed, so plan on the walker itself.

How big is the finished model?

No dimensions are given. With 525 pieces it is a compact AT-AT, small enough to sit on a shelf alongside other LEGO Star Wars sets.

It depends on what you want. If you want a large, detailed AT-AT, save for the UCS version. If you want a recognizable walker at a modest size and piece count, this fits.