I have built 13 3d wooden puzzles, about 8 from UGEARS. UGEARS kits use the most finished plywood of the 3 brands I have built. The instructions are the best and easiest to follow.. UGEARS uses rubber band power while another brand uses springs (rubber bands are the best in my opinion) These kits although functional are not toys but more for display. I now have a large display and 5 or 6 more kits to assemble.
If you are looking for a new challenge and Lego Technic has become too expensive for you, then UGEARS 3D wooden puzzles are for you.
Caution; when assembling the kits, take extra care when building the gears because sometimes they do not function properly by the time you reach final assembly (sanding & greasing, and taking the crowns off the gears) are key!