Side buttons: present and usable — the side-clicks register reliably but sit a bit close to the shell, so accidental presses can happen depending on your finger placement. (You mentioned “has side click” — this matches community photos/specs.)
Build / rigidity: the ProMax feels less rigid than the U2 Pro (the Pro being the stiffer model). If you press on the shell it flexes more than premium mice, so it doesn’t convey the same dense, solid feel as higher-tier models. (This corresponds with community impressions and product positioning.
Coating: the outer coating is relatively thin — smooth and low-friction (often advertised as “Ice Feel” / smooth coating), but it can feel less durable and less grippy than thicker, textured coatings on higher-end mice. If you sweat a lot or prefer tackier side grips, you might prefer a mouse with rubberized sides.
Summary (quick pros & cons):
Pros: very lightweight and nimble for claw users; flexible connectivity (2.4G / BT / wired); good value for price.
Cons: not as structurally rigid as the Pro variant; thinner coating that may not feel as premium or long-lasting; side-button placement can be hit-or-miss for some grips.