All of the Power Miners toys offer a challenging but achievable level of complexity. Our 7 year old can build them with encouraging supervision and minimal adult interference. The models 'do things' - drills turn with the wheels and cranes operate.
Once built they are fairly durable and can withstand fairly vigorous playing without falling apart, like some Lego models regularly do. You get a lot more for your money than, say, Lego Star Wars toys where Lego have to pay a licensing fee.
Power Miners are of the same scale as other Lego, which makes role play using other Lego themed models, such as Mars Mission, Aqua Raiders and Lego Agents feasible.
There is a good range of larger and more complex Power Miner models and the Command Rig is a recent addition. There are not many small, pocket-money sized models available in the range.