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I use the RP jrx studio units with my WL-x1600(3), (and 580ex2 via rp cubes). my gripes are that the adjustments have no detents or markings, so returning to a setting has no real positive feedback. the knobs are a bit easy to turn as well, so bumping them is a drag due to the lack of 'positions'.
you'll want a set of back up 123 type batteries that each unit requires.
aside from that, I find them totally reliable. I've never tested the range beyond 20 feet or so.
one day I might add some orings behind the knobs to add some resistance in turning them, but I haven't bothered yet.
the jrx transmitter has no hot shoe lock, if that's important to you.
another note about the transmitter is that the knob adjustment is live (you can see the adjustments in real time via the model lamp) and the transmitter need not be on the hot shoe to make adjustments. so you can use the transmitter to make adjustments without needing it to trigger the flash units in case you need to mix trigger brands for whatever reason. simply set the wl/ab units to trigger via the slave function. keep in mind the cubes don't have any slave function if your mixing in the 550ex as well, you'll need the jrx transmitter mounted in this case.
RPs are the only adjustable units I've ever tried with my WL flash units, so I can't compare them to any others.