Because no license is required for these bands, vendors limit output power for spread-spectrum devices in an effort to reduce the potential for interference between radios. From an implementation standpoint, 5.8-GHz products have the advantage of greater available bandwidth and, at least for the near future, less congestion. Operating an unlicensed radio carries with it the obvious risk of interference from other unlicensed operators in close geographic proximity to your sites. Of course, there's no absolute assurance that interference will not take place on licensed frequencies, but in those cases, you at least have legal recourse.
Vendors vary somewhat in how they take advantage of available bandwidth and deal with interference.
The other vendors use direct-sequence signaling. Most of the vendors recommend the use of high-gain directional antennas with their systems. With such a narrow beam, the probability of interference is quite low, and even if it does occur, there are strategies for correcting the problem, including using alternate channels in some cases or reversing the polarization of antennas. None of the vendors manufactures its own antenna. Other vendors offer antenna and cabling packages or provide recommendations for products from third parties.