The iQ5, along with the Q4, were an early attempt at a compact slimline floorstander that delivered. While they were ok, they didn't cut it. They were fine when used in small mode on an AV amp, but lacked low end and warmth when used in two channel mode.
The iQ5SE has been much improved over the iQ5. They actually sound like they have the bass of the iQ7, which was a major step forward. They're still a little lean sounding compared to the competition, but that has always been KEF's signature (until you get to Reference of course). Compare tham against other manufacturers usually not so insightful, lacking the reble and midrange detail of KEF's UniQ driver.
For the price that the iQ5SE can be had for, which is only slightly more than the iQ5's, it's a no brainer.