I haven't played guitar since my early twenties (well over twenty years ago) but am now looking to get seriously back into it. Back then all I could afford was a really nasty cheap plastic wah-wah pedal and a 'fuzz' pedal of the same quality. I'm amazed at the variety of pedals available now. Some have fairly obvious uses but what is a constrictor/compressor? Also I've heard various great things about:
1. Ibanez tubescreamer
2. Electro-Harmonix English Muffin
3. Marshall Bluesbreaker

From what I can see these are all distortion pedals achieving the same goal by different methods. Is that correct or are these pedals distinctly different from each other?

Thanks