The TrencherPro Cart is not a must but is an extremely helpful add-on. The trencher it's self is very maneuverable but can be tiring to use on long stretches. The TrencherPro Cart allows the trencher to be used without holding it which can be difficult for some. The trencher attaches in seconds to the trencher cart and will increase productivity, reduce effort and help maintain a consistent depth.
The TrencherPro cart works on the current versions of Terra Trencher and Geo Ripper Trenchers at a fraction of the cost.
A video of the trencher in action can be seen here.