In general, I prefer dealing only with the lady I am seeing, not an organization.  

My one experience with an agency was at an M&G in Vegas several years ago that they were co-sponsoring along with usual group of hobbyists and providers that hold events out there.  What struck me off the bat was that the agency instantly approved me to attend, without the screening the Vegas group did on their own.  I did not see any of the ladies from the agency that week-end, since I had indy friends also there that week-end that I saw instead, but there was no reason not to...several of the agency's ladies were in attendance, and they were as hot and personable as the indy ladies.  Still, after the week-end was over, the agency put me on their mailing list, and sent a number of advertising e-mails.  Then, there were two really big agency busts in Phoenix, which is where the agency I had contacted was based.  Although they were not part of the bust, and dissolved afterward, the fact that they had my e-mail addy, plus the fact that the busted agencies kept detailed databases regarding their clients' that fell into LE hands, did cause me to think twice about agency practices, since they all seem to keep detailed records that are a treasure trove to LE.  

Since then, as before, indy's only.  There are no shortage of them, and there are several I can meet with at any time depending on scheduling, plus a few I have met at M&G's that I would like to see in a more personal settling...