It depend mostly on the music, that type of slider can be funny or awful if the music do or not hint it's gonna vibrate. Like this the compression is about 10-20% ( the slider is a bit shorter than normal, but a bit more fatter than other sliders ) 2x1-3x1-2x2 grid 4 zig-zag vibrate slower (are are even more fatter). In fact, if the slider is arleady slow, the vibrato do effect the graphic, but not that much the length (in case it's used in easies, the speed change is barely noticeable, usually); differently, when used in harder difficulties it's actually noticeable, but harder difficulties player are supposed to see the slider is fattier.
It shouldn't be prohibited, it have to be controlled on a case-to-case basis by different kind of modders and still, it was considered rankable with this rule (that prohibited going back and forth on the same place to "slow" or following abnormal waypoints placement that slowed part of the slider)
I usually use it when it can be used, and since I didn't map that much lately ( university exams, I started to sing, etc ) and especially, I didn't map many songs that would accept that kind of sliders.