Originally designed for the Keylab 88 MKII, these legs not only have a perfect and beautiful look and feel, adding a complementary elegance to the keyboard, but they add a solid level of stability, are super easy to install, and can easily be put on and off, once the plates are installed.
Having said that, it's not as easy as putting the keyboard on a stand. You have to turn the keyboard on its side to add or remove them, and considering its weight, it might be something to consider if you need to constantly put them on and off. Their adjustability is also highly limited, which may affect those who want their keyboard to be higher up. The legs really put the keyboard at a piano height, and if that's your thing, they're perfect.
As it pertains to space considerations. They protrude about an inch to each side of the Keylab 88 MKII and around 4 to the back, more or less (I'm visually estimating, not measuring). I can't say as to how it looks or how much space it takes around a Polybrute or others.
In summary, the legs are a solid product, well built, and add beauty and stability to an already good looking, and solid product.