There is another advantage to the new P'lenses. On the old lTM version you had to remove the hood to attach a filter (39mm) and, particularly with the chrome ringed Leica 39's there was a fair chance of reflective flare from the ring. The new P hood will take a 39mm filter and still screw on to the lens.
I dont use filters very often, but with black/white i carry a yellow/orange/red set along. The round hood on my LTM lens always got lost in my bag so this new hood is an improvement. The square hood does intrude quite a bit, but it does look good. The LTM 21 is back on the Bessa T, the 25 LTM is back on the Bessa L and the 21/4 P has been on my R4M since I got it in March. I did a couple of rolls with the 25/2,8 Biogon and the 28/2,8 Biogon, as well as the 38/2,8 Elmarit and the 28/1.9. These lenses do block the finder in the R4M slightly, but you can use them on them - just "sweep" the area and remember what disappeared in the lower right when you shoot.