What is the use of unique bitcoin address. Will it make you rich.
If you by accident get a different address then use it. If you go for a online service, then that might risk you bitcoins.
It's more of for identification and trend than anything else. There is a high probability that only the first few letter are predetermined. I believe a service called first bits allow the user to know the entire address by keying in the first few letters. I don't get your part about getting a different address.
It's like getting a fancy number for your mobile phone or car... I do not find it's worth. Because address are anonymous already.