Personally, I prefer to use a standalone app rather than an online web service. The online services can very easily retain a copy of the data, particularily email addresses.
I use the QuickMark for Windows app (http://www.quickmark.com.tw/En/basic/downloadPC.asp
) which will read QR codes and can generate them. There are several others out there.
I also use an "extension" that's available for the Opera browser. There are several available that will generate QR codes for the currently displayed page.
I build WordPress websites and looked into a plugin for WordPress that would place a QRcode generator on a page/post or in a widget area making it possible for visitors to create their own QR codes much like the site you list. I was quite surprised how easy it was to harvest data without real programming.