The PW flex’s became a joke years ago*.
Not only is the YN622 system much cheaper, it’s more reliable too.
* though there are a hardcore of ‘brand’ fanboys who refuse to accept this.
Everyone I know who used them, sold them and replaced them with Yongnuo.
Though gradually we’re now all moving to Godox.
Definitely look at the x1n receiver compatibility with the SB900 too.
PW lost the plot when they introduced the FlexTT5 TTL radios. Before then, they were just overpriced. Back in 2012 when their new TTL system came out it was the flakiest thing ever. Even Joe McNally, who was working with them couldn't get them to work reliably and said as much (on page 237 of "Sketching Light"). He even put together a "startup procedure" that he'd found had the best chance of the different bits talking to each other. It reads like a Voodoo ritual and includes things like "Turn your lens VR off" (!) and "Use the 'top down' turn-on sequence religiously. Flash, Flex, Mini, camera". Yeah, like I'm going to do all that in the middle of the Krypton Factor that makes up most of my shooting experience (ie I have one maybe two goes to get it right before the subject wanders off...). I also remember at the time when I looked at getting these (TTL over radio back then was akin to the Holy Grail - most radio flashes were trigger only, and almost all of the more complex ones were proprietary systems for big lights - and even then they only allowed remote manual power adjustment) was that even if you bought a couple of FlexTT5s or a Flex and a MiniTT1 transmitter, you needed to buy another shonky looking widget called the "AC3 Zone controller" that sat on top of the Flex and allowed you to dial in compensation on the 3 flash groups. As I had Nikon cameras and flashes which even back then could do full TTL or remote manual using either the pop-up twinkle light or a camera mounted SB800 or 900 to send the data and commands, this just seemed like a complete lash-up, and an expensive one at that. Sure, radio would be nice as the Nikon system used flash pulses. It's a myth that they needed "line of sight" tbh as it would work just fine with the master flash signals bouncing off walls, floors and ceilings around corners but in some scenarios (high ambient light levels, or just no route for the light to bounce around) it would not work.
View: https://www.youtube.com/watch?v=vfTR3QtbDbU
You could get around it by putting the master flash on the end of an SB28 cable several metres away from the camera - and these could be daisy chained - to allow the master to be in a better place to instruct the flashes and Joe's books are full of such lash-ups but hey - I wanted simple! Pocket Wizard's Flex system though, looked just as complex, and, if anything, less reliable.
When the Yongnuo 622's came out - I didn't really do any such research as they were £25 a piece. So I bought 3. I went at it lashing 4 SB900's to one YN622 via a 4-way PC-Sync cord to freeze some dance shots
http://owenlloydphotography.com/?p=1266 It worked wonderfully, and I didn't need to adjust the power for this - it was bound by the flash duration and so all of them were on 1/4 power - permanently, to give the equivalent of a full power flash at 1/4 power duration. The new radio triggers allowed me to trigger them inside a softbox, every time. However, these YN622 transceivers (the trigger is the exact same unit as the receiver) had no screen and adjusting the power of TTL compensation of each group was a done via semaphore and reading runes. Actually, no, there were no runes - you had to remember how many clicks you'd done in each group, after doing the little dance to select each group. I never used them like this: I couldn't afford to get into that maze with a subject in front of me.
A few months later though - Yongnuo fixed all this with the release of the YN622-TX - a dedicated transmitter with a screen on it, and cursor buttons.
http://owenlloydphotography.com/?p=1525 I now have 6 YN622's and a couple of 622-TX's and it all works. If it does ever glitch - its always a battery issue for me - just replace the cells and of you go. Another nice touch on the 622-TX is it comes with a cable to connect it to the camera control port on my Nikons, which means I can fire the camera from any of the flashes using the test fire button on the YN622 receivers, or just hold another receiver.
Now if I was buying triggers Today, as Phil said, I would go for the Godox ones (and in fact I do have a Godox X-pro trigger, but haven't bought anything to trigger with it yet
I just wanted to have a look before migrating everything to it). They have the same capabilities as the Yongnuo system but, they also control almost the full range of Godox lights from Speedlights to full size studio lights and all of the wonderful portable options in between - all from the same X-Pro trigger (you can't control the power on the older Godox studio lights even when fitted with the new 2.4Ghz receivers - it's trigger only and I don't know why - all the hardware is there). I may buy x1n's for my fleet of SB900's however it may be better to sell them all and replace with Godox Speedlights and a couple of AD200's (the receivers are built in on the current Godox lights, so less set-up time and less batteries to worry about).
