Disclaimer: I'm a Backblaze employee. Backblaze tends to be extremely simple to use. After installation, you enter your email address and a password (on the client side) and you are now CORRECTLY configured. By default, Backblaze backs up any and all files on your computer. You don't have to pick and choose folders, write a script, setup a second computer at your Mom's house, nothing. There are only 3 billing options: $5/month (utterly unthrottled and no size limits), or if you pay for 1 year up front it is $50, pay for two years it is $95.
Simple and "just works" makes some customers happy, but Backblaze isn't perfect for everybody. If you like playing with your backups, scripting them, configuring machines, excluding folders - Backblaze will drive you crazy as you fight to control it. For example, if you add a new folder of images to your computer, Backblaze will push them to our datacenter unless you EXPLICITLY exclude that folder. Some customers would like an option that all new folders ARE NOT backed up until they "add" them to the backup. Backblaze must be thought of as a complete solution - if it doesn't fit your needs, we can highly recommend other more scriptable products to you.
There is no shame that we only fit the needs of a subset of customers, our biggest challenge is communicating what we do and do not do clearly so we don't waste your time.
The original question was "with these flaws why use Backblaze?" The answer is, only customers who view these "flaws" as good things should use Backblaze. For example, your files are encrypted at Backblaze and we absolutely don't store your password. But by default, you can "recover" your password with access to your email address. You can enable a higher level of security on Backblaze where you can NEVER recover your password and if you forget your password, you are screwed. This is NOT the best option if your Mom is using Backblaze to backup her cat pictures. Friendly and easy is a BETTER solution for some people. But if you are really, really concerned about security, look into Backblaze's "private encryption key" option.