All models require the drives to be screwed to a cradle as far as I am aware; some models eg. the 409slim have the cradles accessible via a simple catch and slide-in arrangement, some like the 710+ also have a catch and slide-in arrangement and are hot-swappable, others (mainly the single bay units) require minor disassembly of the casing with a screwdriver, while others such as the 4-bay 411+ need a panel removed by thumb screws, so quite a variety but none of them very difficult.

Unless you needed the hot-swap ability or are changing drives frequently, I would not say that it would be a major consideration.