This is very expensive alfalfa seed. I think they overestimated what the market will bear and acreage that needs herbicide treatment. When weeds invade an established stand, it usually means poor management and/or the stand is declining and needs to be taken out. Applying a glyphosate herbicide may increase quality, but decreases yield. The only advantage that I see for RR alfalfa is 1st cut seedling year weed control. A companion cereal crop for weed, erosion and leafhopper control can best be removed with a grass herbicide. An herbicide such as Raptor will cause crop injury, but there are other herbicides or the entire field may not have to be treated. There may be a few instances where glyphosate alfalfa may work for some particular weed problem. However when considering the over use of glyphosate and the developing glyphosate resistant weeds, that the perennial mature of alfalfa making good stewardship practice difficult, the seed size similar to many weeds resulting in potential spread of resistant weeds, the introduction of RR alfalfa does not seem like a good idea. It seems to me that the introduction of glyphosate resistance into alfalfa will hasten the development of resistant weeds destroying the value of this effective inexpensive herbicide. In addition; you lose glyphosate as a means of taking out the stand. If you are considering RR varieties, check for yield against regular varieties. It is surprising they released and produced considerable seed when the only independent data is seedling year data. You may be paying a lot for weed control in the first cutting with lower hay yields for the rest of the life of the stand. You can find some yield data at the following sites.

http://plbrgen.cals.cornell.edu/programsandprojects/departmental/foragetest;
Table 1: Alfalfa trial at Ithaca, Tompkins Co., Sown April 29, 2003
Table 2: Alfalfa Trial at Chazy, Clinton Co., Sown May 13, 2004

http://varietytest.unl.edu/alfalfa/2006/HAVELOCK2006table06.htm
Havelock, Lancaster County, Agronomy Research Farm

http://www.ag.ndsu.nodak.edu/plantsci/forage/perftest.htm
Table 4) Marshfield Wood County

http://plantsci.sdstate.edu/forages/Alfalfa%20Trials/SD_Alfalfa_Trials.html
Brookings, SD

http://www.css.msu.edu/VarietyTrials/Index.html
East Lansing, Ingham Co.

http://www.oardc.ohio-state.edu/forage2006/
Wooster, Ohio

http://alfalfa.okstate.edu/var-test/2006/501-2006.htm
Stillwater, Agronomy Research Station, Payne Count
Chickasha, Central Oklahoma Research Station, Grady Count
Perkins, Agronomy Research Station, Payne County

http://www.croptesting.iastate.edu/alfalfa/results/
Nashua, Floyd County, Northeast research farm

http://www.idahohay.com/06alftrials.pdf
Rexburg, Idaho