Flatbeds are a compromise by design, I'll take a dedicated to scan my 35mm and nothing else....every day of the week, rather than be able to scan other things with a flatbed.
Unfortunately, flatbeds are pretty much the only option for LF, even dedicateds that scan MF are daft expensive so a flatbed will see you do all those and still allow you to.....eat.
I actually envy 35mm shooters because a dedicated for 35mm is the cheap(est) and easiest to acquire....I wouldn't call em cheap though.
I have a Minolta dedicated, it scans up to 6x9 MF, its at least a thousand years old but keeps on chugging, so that augers well for your 5400...