Tube style sights are bigger, heavier, and generally block a bit more of you field of view. They are easier to learn to use because the alignment is more intuitive. The emitter is enclosed so it will not get dirty and your reticle will not become dirty.
Reflex style sights are lighter and block less of your field of view, alignment is less intuitive but you can train yourself to get past that. Since the emitter is exposed, it can be blocked by dirt and other #### that might get to it. You will also be able to see the reflection of the debris near your emitter, which can be extremely distracting.
Simply put, if you are indoors and only shooting paper, a reflector is probably better. If you are doing anything outdoors in a non sterile environment, you will want an enclosed optic.