Judging by the date alignment, it looks almost certain that REI contracts with Shasta Mountain Guides for REI's Shasta trips.
With that knowledge, you can better compare Shasta Mountain Guides ($,dates,agendas,goals) with Alpine Skills International and SWS Mountain Guides. http://www.rei.com/adventures/trips/wee ... _wend.htmlhttp://shastaguides.com/climbs/http://alpineskills.com/cat_shasta.htmlhttps://www.swsmtns.com/
BTW, what EB said is correct. Sierra Mountain Center is a top notch group.
However, it doesn't look like they officially hold a use permit with Shasta National Forest to do guided climbing on the mountain. That being said, I'm sure many of the SMC guides have "company relationships" with the current three that do. So if you have a specific guide in mind, it's possible that that specific guide may work under the company holding the NF use permit. Usually, the best thing to do is call the guide service and tell them what you are interested in and see where the conversation goes.
EB-chime in if I've missed something or have gotten something wrong.