I too use a Combi plan tank, having got lots of neg scratching with a Stainless Nikor tank. There are quirks which annoyed me to start with, but it has now trained me and we get along fine! Main thing is long time needed to pour in chemicals as noted previously, but to no adverse effect. I pour in and out through top vent to keep times as even as possible. Despite this, development is even. Once fixed, I remove top and fill far more easily for washing, pouring water onto central bar to reduce impact on film.