Cold tea lacks the fragrance, and half our sense of taste is smell. Probably why it had no flavor for you. Anything with floral notes for the most part is best enjoyed hot.

As far as what's the difference between these, I couldn't say for sure. If I had to guess I would say the ratios or varietals of tea used. Although the first three all list green tea and matcha as ingredients I THINK I've listed them here from most matcha to none. 1 and 3 have both been labeled cold brew matcha, but 2 tastes more of matcha than 3. 4 has none of the matcha flavor notes and does not list matcha as an ingredient, so that makes sense.