I have a small cultivator - 5 hp engine which drives 2 rotating flails producing about a 2ft width of dug soil.
I offer this assessment of its performance to anyone considering getting or using one.
My land is light sandy soil which drains very easily. It is best to use the cultivator on it when the soil is damp to wet.
Yesterday, it took me 4 hours of fairly hard work to dig over an area 10 metres by 30 metres. It used about 1 litre of petrol (a full tank) to do this.
The top layer of the soil was slightly compacted with a thin covering of weeds. The few grassy patches reduced progress to about half.
The soil was probably dug to a depth of about 4 inches. A second pass (best at right angles to the first) would increase that to 6 inches which is slightly less that you could achieve with a fork or spade. However, the extra depth means that the machine tends to dig itself into a hole making progress slower than you might expect.
Just to be clear this type of cultivator does not have powered wheels. Progress depends on its rotating tines trying to act as wheels and roll forward while they break up the soil in front of them. This type weighs about 60 kg making it transportable in the back of a small van or estate car while the type with powered wheels weighs around 90 kg. This is fine if you can store it local to the land on which you want to work but rather heavy to lift into a vehicle.
If you have to work with heavy clay soil, I think you would find the heavier type of cultivator with powered wheels better on compacted soil. However the lighter type (like mine) might still be suitable for turning over seed beds and vegetable plots which are dug regularly.