I just invested in a set of Stratos II triggers and couldn't be happier. To clarify the original poster's question, the Stratos series does "TTL pass through" instead of transmitting TTL signal. That means when you put the transmitter on your camera and a flash on top of that (either directly mounted or with an OC-3 cord), the mounted flash works just as if the Stratos weren't there, so all TTL functions work correctly. The remote flashes however, only get the flash trigger and no TTL info. The Phottix Odin series does transmit the eTTL signle I think, but I never really desired to have my off camera flashes in auto mode, so I didn't go that route.
This is exactly what I was looking for when shooting events with on-camera and remote flashes. For a wedding reception I shot a few weeks ago, I set up 2 remote 580exII's on stands in the corners of the room and manually dialed them down to 1/16 or 1/8 power and used a 600ex-rt on-camera in normal eTTL mode. This configuration worked flawlessly and I couldn't have been happier with the results. The push-button setup on the transmitter to activate groups superbly designed. I can turn on/off the remote flashes individually at the push of a button for each. The Stratos II series wakes up the remote flashes as well, so you don't have to worry about sleep issues.
I also own 4 PW FlexTT5's. After over $1,000 of investments with abmissal reliability over the past few years, I finally decided to throw in the towel. These do not currently work with the 5D3 and I assume the 1DX, but haven't bothered to try. The Stratos II work perfectly with the 5D3 and 600ex-RT combo. The FlexTT5's are known to have issues with RF noise from the 580exII, but after paying $75/ea to get my 580's modified to eliminate that problem, I still didn't get good results. I will say the FlexTT5's have worked perfectly when used as manual triggers with studio strobes (except on the 5D3 -- that's also a buggy combo). PW states they are working on a firmware upgrade for their products to make the 5D3 work and I've heard other people use the Flex series with flashes other than the 580exII without issues. Right now however, you'll have to wait for PW's firmware upgrades for 5D3 or 1DX compatibility and I still wouldn't put much faith in reliability if you're using 580exII's.
I've used regular Pocket Wizards for years and some of them were ancient. The regular ones are simply the most reliable trigger probably ever made, so I don't want to completely dismiss PW. If you just want a basic trigger, the new PW Plus III is a great investment at a very good price. My experience with the Flex series left me very disenchanted, though, so looked elsewhere for a solution that let me use eTTL. I also didn't want to have to hang something off my camera for a trigger, so hot-shoe mounting (with the option to attach an on-camera flash) was my preferred design.
