The first problem is that they aren't free. Although, I generally get free poweraid when I buy mine.

Generally, I use a poweraid bottle when I backpack. But, when I day hike, I like to take my kleen canteen. I like it's ruggedness, and extra security it gives me. But, it's too heavy. Vargo makes a titanium version that costs a lot. Someday I will probably buy one.
I've taken a vow of poverty. To annoy me, send money.