Meaning if i do multiple transactions using that Instant Exchange and convert Bitcoin to Litecoin. (The destination address of LTC remains the same in all the transactions )
No matter how many times you send bitcoin to the exchanges like exch.cx, they will always give you a new bitcoin address where you will deposit the bitcoin and in return they will send you whichever coin you want to exchange (in your case Litecoin). Usually, each time the Litecoin you will receive will be from a different address. Now there is no link between your bitcoin you have send and the Litecoin you have received.
So, if you are not looking for anything more than that, you can go for
https://exch.cx/. It is one of the instant exchanges that I can recommend.
exch.cx is by far the most economical one to use for these types of transactions but i haven't tested it for any big amount. Their exchange rate is the best, close to the centralized exchanges like binance etc. Usually, it is better to conduct small transactions from these centralized instant exchanges, so the chances for their scam are minimal. No matter we do a multiple 50$ transactions or a one 500$ transactions, the fee will be same (1% Fixed or 0.5% dynamic).