BK are blocks for the fixed end of the screw. That means they have two angular contact bearings to stop axial and radial movement.
BF are for the other end of the screw (floating end). They have a simple ball bearing that stops radial movement but allows axial movement (slides in housing)
FK is the same as BK but a different shape.
FF is the same as BF but a different shape.
Google images for what they look like.
The F series are designed for face mounting (mounting screw perpendicular to a plate) where as the B series are for mounting parallel to a surface but can also face mount.
It's unlikely you can make anything cheaper and better than the Chinese ones unless you have a mill or lathe.
Of note with the Chinese blocks: the angular contact bearings are usually not matched or preloaded properly. On all mine, when I've removed the dust shields there has been considerable play. Taken apart I can get a 0.25mm feeler gauge between the outer races of the bearings. The bearings require shims between them (0.2 to 0.3mm in my case). Whether you shim the inside or outside races depends on which orientation you choose (back to back or face to face).
7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)