My 9 year old daughter wanted a Lego Technic kit for a Christmas present so we gave her the 8257 to start with. It took Hannah about an hour to assemble:
Hannah says: "I'd rate this 8/10, it's fun to make but is not as good as Dad's old Technical Lego Bulldozer because it has less pieces and only does a few things."
Due to the way inflation works, this kit was more expensive than the old 856 Bulldozer and has far less parts, and is a tiny redux of the original. It uses a worm gear mechanism to raise and lower the shovel. Being small, the kit contains a whole load of fiddly clips and brick elements. On the plus side, it contains two model variations which is a bonus.
On Boxing Day Hannah assembled the digger following the second set of plans. Hannah says: "This was more fun than the bulldozer - it can do more things even though it uses less bricks."
The digger cabin is pivoted on the wheel assembly and can rotate a full 360 degrees. The main digger arm is controlled using a worm gear and a lever and linkage and connected to this is a free moving digger shovel. Took Hannah about 45 minutes to build this. Here are some photos: