The naked portafilter is on the rise.
We use it permanentely on one of our group heads. Also Broer Bretel decided to start pulling shots this way and with Slayer equipping all their machines automatic with naked portafilters it looks like it's becoming more then a trend.
The photo is from 4 years ago - you notice a faster pour -when we just tested it on our Faema.
This article from 5 Senses explains a bit more the pratice.