too slippery?

You DO have a steep slope to deal with! The tree roots will help stabilize the soil and make a mudslide less likely. If you cannot mow the lawn safely, terrace the area (think Machu Pichu) into garden beds for flowers or vegetables. Do you want your children to play on a grassy area or on a man-made surface? Be sure that the play area has shade during the hottest part of the day. Best wishes.

Can anyone recommend a product to use on cleaning the units?

My daughter ordered a hobby rock tumbler from a NZ online website. The information on the website stated that the tumbler would be shipped from overseas (USA) direct to her with no warning about suitability or otherwise of the machine for NZ conditions. On opening the box she noted the following: 1. The electric motor was rated at 120volts 60HZ and 0.447 amps. 2. The power lead on the machine had a USA-type three pin plug. 3.The instructions stated that the third pin on the plug was a grounding pin and must be connected to a grounded socket. Obviously the machine needs a step-down transformer to work in NZ. My questions are: 1. Are there 230v to 120v stepdown transformers available in NZ with a US three pin input socket and a NZ three pin earthed plug on the power lead to provide continuous grounding of the machine? 2. What should the minimum current rating of the transformer be to suit the electric motor?