So here’s the sitch:
The standard portafilter doesn’t have a circlip, but the cheap ‘official(?)’ naked portafilter does.
The coffee-sensor naked portafilter does too but it’s a little looser.
The standard basket is a little loose in the ‘official’ naked pf but IMS basket fits beautifully tight. Except it’s too tall and doesn’t seat all the way down. Plus drops catch the lip and go everywhere.
The coffee-sensor pf has a circlip but it’s a little wider diameter. Standard basket is properly loose, IMS basket is held lightly (enough to turn upside down but not enough to knock without something stopping the basket ejecting.
I use coffee sensor pf and IMS basket. I just tap the puck out on to my hand once it’s cooled (so basket doesn’t escape) then bin it and rinse hand and basket immediately.