What does everyone think about the yongnuo speedlites?
They have a good range of models that could fit different budgets and they seem to have good reviews from strobists.
Apparently only yongnuo's most recent models include high speed sync... So if that is a concern your choices in their lineup may be limited to a couple at higher price point... Which may still come below Canon's price range but may not be by much, so I would choose Canon's own midrange slaves 430ex II or just the older 430ex for a few more bucks and have no surprises.
But for a 2nd or 3rd ETTL slave in portrait studio kinda work, I think yongnuo should be just fine.
Does YN have a speedlite that has RF triggering built in that would work with the 600EX-RT ? That would be sweet, no need for extra transceivers.
Bodies: Canon 6D, 70D, T2i gripped, EOS 5, EOS 100, EOS M
Lenses:EF 24-105 F4L, EF 70-200 F2.8L mkII, EF 100 F2.8L, EF 50 F1.8, EF-S 18-55mm, EF 28-80 USM, EF-M 22, Rokinon 8mm HD Fisheye, M mount adapter
Other : 540EZ, 320EX, 430EX II, Yongnuo triggers & strobist stuff