Redundancy in your planning, especially with something as critical as drinking water, is the wise approach.
In my mind--the water purification tablets (chlorine dioxide) are an important resource to have on hand. If they expire on you before you use them, oh well--it won't hurt anything to either try them anyway, or to just throw them away. They are relatively inexpensive and lightweight. Their ability to treat/eliminate viruses, bacteria, cryptosporidium, and Giardia in water is important. Water filters can't purify to that level.
Boiling water CAN do that, but are you sure you are always going to be able to boil water? Yes, it is good to plan to do that. Of course, that means including a pot of some kind in your bag. I'd suggest a mess kit/cook kit.
As for which bottle--I'm a Katadyn guy. But whatever bottle you choose, I'd suggest going with a trustworthy brand name. As with anything, you get what you pay for. In terms of something like this--where your health is on the line, spend a few extra bucks to get the assurance that comes with a recognized, reliable product.