What do you mean by a mining pool with low difficulty?
It's not that each pool has its own difficulty. Difficulty is a value that determines how it's difficult to mine a block and that's the same number for anyone trying to mine bitcoin regardless of which pool they have joined.
Each pool has its own pool/work difficulty because it makes no sense for the pool to process every share your miner finds, it also makes no sense to just submit a share that beats the network difficulty, so pools want you to submit as fewer shares as possible but they still want you to submit enough shares so they can pay you accordingly.
As mentioned, I used to mine on BlockMasters and it has a difficulty of 9050 which gave me a good profit.
Well, using a low difficulty pool just means it accepts more shares from your miner, which is useful in determining your hashrate faster than on pools with larger difficulty, but then when it comes to profit it won't change, because a share at 9050 diff is worth half the share submitted at 9050*2, so at 9050*100 diff you just need to submit 1 good share instead of 100 at 9050.
In some rare cases when using very slow mining hardware, using a lower diff is better since your miner might not find a larger share and won't get paid at all, but if that's the case, it means even at a lower diff your miner isn't making "any profit", and honestly, if you have to worry about pool diff it means you are using the wrong gear for the right coin.
