I haven't done any of my very informal testing of them (I haven't even bought any yet), so everything I say is only from the reading I've done.
The EFMJ's do not expand as large as a perfectly expanded JHP does. But, it does expand the same amount, every time, no matter what it encounters, whether it be a barrier in a house (sheetrock can clog up JHP's and cause them not to expand) or flannel or heavy clothing (which can do the same thing as sheetrock to JHP's). According to the last article I read on them, they expand the same amount, every time, no matter what barrier it encounters, and has the same penetration distances as it's JHP counterparts.
Since there are so many factors which effect a JHP's expansion, the EFMJ seems like a more reliable substitute, to me anyway. No, it doesn't have the talons the Ranger SXT's do, but it does expand, all the time, and causes a permanent wound channel, every time.
Again, I'm far, very far, from being an expert. I'm just repeating what I've read in magazine articles and online from companies who have done ballistics testing.
Again, from what I've read, there are not a large number of documented self defense shootings involving the EFMJ round, but from the ones that have been documented, they react in the real world the same way that they do in testing. The article showed one round which was recovered from an attempted rapists chest, fired by the woman from a Glock 19. It was the 124gr +P EFMJ round.