I have tripod and heads/quickrelease clamps with build-in bubble level. They works perfect if horizon parallel to the camera. But what if need to swing a camera up or down? Then bubble goes off-center. In such cases (and it's 99% of all the shots) I need to use two axis hotshoe bubble level or I just don't understand something and it's possible to use that build-in level somehow? If no, I have no idea what's the point of build-in level, if no use for 99%.

The bubble level will give you both horizontal and vertical leveling if that is what you want--if you put the bubble in the middle of the circle it will be level both directions. This can be useful for some shots. It can also be useful to start with a level base like this and add a panning base for panoramas (for example, it makes using the RRS pano kit a lot easier). It does have its limitations. If you want a horizontally level shot, but not a vertically level shot (e.g., the camera is pointed slightly down), then it isn't of much use. I guess it all depends on what type of shots you want. I use it about 10 or 20 percent of the time when I am setting up landscape shots.