So here's an update on the device: I have found that my re-purposed 16" wheeled folding bike, given it's small turning circle, is also most useful around the house. It's like a highly manoeuvrable stool that takes the weight off my osteoarthritic knees and permits almost pain free household activities (cooking, washing, etc). The 4 wheeled Zimmer and crutches in the photo are almost redundant. The bar bag mounted on a cheap front rack is really useful for transporting goods to and fro from the allotment.