Practicing with metronome is very useful to keep a steady tempo. You can also use it to learn difficult passages by playing slowly at first and gradually increasing the speed. Since there isn't much difference between let's say 60 and 64, you won't feel you are actually playing faster. Once you're good at 64 then try 68 and so on until you reach the desired tempo. You'll be amazed how quickly you can learn hard passages this way.
You will achieve a lot more by dividing your pieces or etudes in small sections and practicing each small part individually. Your brain will develop the right reflexes faster by repeating the same passage many times until it gets it right just like a martial artist repeats the same movement over and over again until he/she doesn't have to think about it. You can put all the bits together afterwards once you've thoroughly worked on them separately.
I am associate principal horn of the Singapore Symphony Orchestra and the author of the progressive methods. I'm happy to share my experience as a horn player and teacher with you.