I made one for my Gaggia and La Peppina and I think the better question is,
why should you use a spouted portafilter? I can't think of a reason in the world. (Other than if you're splitting shots, which I never do). Is there any argument that after the espresso is made it is good for it to go down less than clean metal channels, get split into two and land in the cup? Is this post processing of coffee any advantage at all? If it is why not attach a pipe to the spout and make it go a bit further-- maybe over to the sink so you can avoid cleaning the drip tray.
On the plus side of nakeds: less cleaning, no buildup, easier to tamp, can put in a triple basket (I have to see if I can find one that fits the Peppina), nice to watch if you feel like it, more cup clearance if you need it, no need to preheat the portafilter, since it is not robbing much, if any, heat from the coffee.
So, given the above, what advantage does the spout offer? I don't see any.
dan
...split from New perspective on value of the naked portafilter by moderator...