These implements aren't widespread like other tractor attachments, but are popular with farmers who want to have a tractor that can do basically every job on the property. While they are simple in design and use, they are incredibly effective at what they do and will make lifting and moving heavy loads a lot easier on any property.
The lifting capacity of your tractor crane will depend on the exact specification of your machine, as well as the counterweights available. To help improve stability and lifting capacity, some tractor cranes have stabilisers that lift the tractor off the ground. This takes the weight off the tyres and axles of the tractor and spreads the load out evenly.
Of course, there are many brands that manufacture tractor cranes as a whole machine, rather than just as an attachment. These offer a little less flexibility in their use, as it's harder to switch to a full range of tractor implements however, they do generally offer a larger lifting capacity and are better suited to lifting and moving heavy items than a traditional tractor.
Many of these tractor cranes are able to make use of a range of implements, either by attaching them to the tip of the crane arm, or using a 3-point attachment on the tractor.
If you're looking to buy a tractor crane or attachment make sure you have a clear understanding of the requirements of the work you need it to do. If you're after an attachment that will do the job, discuss with your dealer or seller about the compatibility with your current tractor and the lifting capacity it can handle. For complete tractor cranes, make sure you know what other implements they can utilise as well.
Whether you're buying an attachment or a whole tractor crane, always consult with your dealer or seller about warranty, lifting capacity and other specifications before buying or hiring.