There are a couple of things to keep in mind with these tanks. Try not to use the small hole in the top for filling. If possible, use the tank with the lid off in a dark room for filling of developer, then set the inner holder in place with presoaked film. Filling can take a bit of time.
A staining developer (PMK) can cause uneven development of continuous tone areas (clear blue sky). I was never able to use the tank with PMK in this situation, even with shaking the s*** out of the tank every 15 seconds as recommended with PMK. It was subtle, but evident in the sky areas, as we seldom have clouds here most times of the year.
You need to be able to pour chemicals rapidly to keep from getting uneven development.