I would have thought that the Pure Freedom was probably the most compact professional trolley out there. I've had mine for 5 1/2 years and think it's brilliant. The only improvement I can see would be to make it out of a lighter material. However, that may push the price up.
Mine goes in the boot of my Nissan Primera saloon with six barrels of water which keeps me going for four hours straight doing ups and most downs.
The only thing I've had to replace on it is the battery. They seem to last about two years. I've just replaced it with an equivalent Lucas AGM battery.
Here is a picture of my trolley in the trunk of my car with five barrels of water. It will go in with six. It shows how compact this trolley is.