You will have a lot of trouble speaking for the first few days or week that you get the tongue piercing. You will not be able to eat normal foods and will have to mostly eat liquids. But the after a little while, you will not be able to notice that you have one.
Your new piercing will take a little while to get used to. You may speak differently, more so because you know it's there. Also, be careful of chipped teeth, it happens easily.
They are very obvious. Once your tongue is mutilated, you will never talk completely normally again. You will also damage the enamel of your teeth and have more mouth diseases because of all the germs you can't brush out. There's no way you can keep all that hidden.