Davor,
All systems have positives and negatives.
Above ground systems using stakes and guy wires can cause trunk damage if not attached correctly and removed as well as are unappealing. Also, we have to assume that the contractor will continue the maintenance and removal of the stake and guy wires after the site is turned over to the owner. Though they are the cheapest of the systems, they also produce tripping hazards for pedestrians and can be problematic for lawn crews when mowing and trimming.
Anchor rootballs below grade eliminates the above negatives but you should choose the system that best suits the project and selection of trees. You should look for what materials are being used on the system and what kind of footprint will be left. Also, the be aware of what is being used to provide tension to the top of the rootball and whether the rootball has the sufficient strength. Sheering the rootball is common when anchoring with straps so be conscientious with the type and width of the material that will spread the load on the root surface. Thick materials that do not conform to the shape of the rootball can commonly begin pushing through the nursery line and heave the ground above creating an eyesore and tripping hazard.
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