I see your point. The conical bottom will create a small, deep plug for a yeastcake instead of a thin widely spread yeast cake. Which will affect the fermentation and flavour, etc. I think these are just a fad myself. Redesigning the fermentor to harvest yeast is redundant. It's simple to harvest yeast with a traditional type fermentor, and simple to remove it during fermentation ( which may not be beneficial ) by transfering to a carboy. Although i'm sure there are supporters of these conicals, to me it's just a marketing ploy creating a solution for a problem that doesn't exist.
I thought about using them for awhile, and decided against it. Too restrictive for me. I decided on a spiedel 60 liter fermentor with a dispensing spigot. It's all I need, and I reuse yeast and propagate it very nicely, quickly and easily.
When you consider things like : Cleaning, footprint, storage, capacity for 5 to 15 gallons plus headroom, mobility, simplicity, sanitation, Yeast cake functionality, Cost factor, and just plain ease of use; to me the Spiedel 60 liter is the one to have.