There is an important difference between Master Merchant and the Tamriel Trade Centre AddONs.
Master Merchant (MM): Provides you with the average price that the item you are interested in has sold for from the Guild Stores you are able to use in game over the period set in the settings.
Tamriel Trade Centre (TTC): Provides you with the recent prices that users of TTC have reported seeing the item you are interested listed on Guild Stores they have visited in game.
So the key differences are that:
- MM gives you the price people have paid for the item, whilst TTC tells you what other sellers are asking for it.
- MM only reports on the prices paid in Guild Stores you can use (Max 5 Guild Stores), whilst TTC gives you information on a random number of Guild Stores.
- MM has no global search option, whereas TTC has a web search function that can identify which Guild Stores currently stock the item you want.
I don't think there is another AddOn that does exactly what MM or TTC do, and they don't do exactly the same thing as each other.
Hope that helps.