Do you know which ones and why? I'll add it also to my OP.
I can't reproduce the details of "why", but you can quite easily test it: just take a prefix and change the first character.
Adding more "ones" (1111111) makes it much harder to find too.
Ok, nice to know, also added to my OP. And I've added some real addresses.
I read the OP, and will read it again carefully to comprehensively catch your ideas.
By now, I am curious that whether the approach will create higher secured address than others created in Blockchain.info's BTC wallets or not.
Would you mind clarifying a little bit more about the most advantages of vanity address, please.
The split-key process and the guide to turn off Internet connection before creating vanity address, spliting keys are valuable one.
Security of your vanity address depends on how you create it. If you create it while your internet connection is active it might be insecure and I don't recommend it. Like LoyceV said, security is very important and it also depends on how much BTC you want to send to it.
If you import it in Electrum, it won't be safer than Electrum anyways...
Creating vanity addresses is normally not the first reason of getting an address, which is much safer than others. It's more a reason that you create an unique address and can use it for example for small payments. However, it's still possible to create very secure addresses with vanitygen but in my opinion the main reason vanity generators were developed for the ability to genereate customized addresses and add a prefix.