...in my experience, I agree that they need less gain...I use both the ES-57 and ES-58 and I find that they definately require less gain and therefore are more likely to go into the red (distort) if pushed too hard...
...but if you use them discretely, and forget your reference level settings for the Shure versions, you may find (as I have) that these mics have more "presence" than the originals...I use both in live applications, and both (IMHO) are capable of out-performing the Shure versions...I much prefer the ES-58 for male vocals, but you do have to back off on the gain levels...the ES-57 also has higher output and will distort if you ride the gain...but if you back off on the gain, both mics have a kinda "in-your-face" presence that makes them great for live gigs as well as recording...
...in fact, I have purchased quite a few of these for other singers, drummers and guitarists that have come to our live gigs and and wanted to know where they could get them...and I've never heard anything but positive feedback from the musicians using them (and I'm talking about pro-session players not garage band kids)...I highly recommend them as an addition to, and often a substitute for the original Shure versions...
...now if I can only convince GLS to manufacture an ES-7B (SM7B clone), that would be way cool!...