Some electricians don't like them, either. I think they're confusing them with connectors on the "back" of light switches, which tend to produce a lot of callbacks. However, I tested these types of connectors by attempting to pull out wire, and it's hard to get wire out of them. You have to rotate the connector while pulling on the wire.
One problem I've had with these connectors is using stranded wire in them and then trying to remove the stranded wire. That can be a bear. A lot of X-10 type switches have wiring that's stranded, and now that I'm moving out of my house and removing these switches for the few ones I've used with the connectors, it's a pain in the butt to get the stranded wire out. It's possible, but takes work.