That reader advertises being the fastest at 20mb/sec, but the Sandisk Extreme IV reader and card combo reads at 40mb/sec.
I took the same group of raw files off a III card and also a IV card through the Extreme IV reader into my Macbook Pro. The III took 40 seconds. The IV took 10 seconds.
Also, the express 34 slot is spring loaded. So if you attempt to leave the reader installed, when you go to push the CF card in, it will also eject the Express card.
Of course, I have not used it. If you end up trying it though, let us know.