ProtoArc's EM25 is a $50 wireless ergonomic mouse built to look like a Logitech MX Master and priced to undercut one.
The EM25 checks the visible boxes: ergonomic chassis, extended thumb rest, dual scroll wheels with a clutch on one, and quiet main clicks. The problem surfaces the moment you start using it. Secondary buttons feel awkward, the scroll wheels lack refinement, and the mouse skates (the plastic feet underneath) feel rough enough to drag against the desk rather than glide across it. The chassis has real structural solidity, which keeps the EM25 from being completely dismissible, but the gap between "has these features" and "executes them well" is significant.
Logitech's MX Master 3S runs around $100, so the pitch for a $50 alternative addresses real demand. The problem is that at that price, you're also competing with well-built standard mice from established brands, none of which need an ergonomic form factor to justify themselves, and most of which feel far more considered than this. If you need the specific shape for comfort reasons and truly cannot wait to save up, the EM25 has something to offer; otherwise, the money goes further elsewhere.
The EM25 is a useful reminder that cloning a product's silhouette is the easy part; the reason people pay for the original is everything the spec sheet doesn't capture.