I purchased this size because I needed something lighter than a 2L and something that would hug my back.
I Love this thing! the 1.5L bladder is just enough for about 2 hours. I usually ride for around 6 hours so I ride out to refill it but on the trails it is great. super light and the front pocket is just big enough to put my phone in.
the only downside that I have for this is it does not have a buckle on the front ( as the larger ones do) so when I get air it slides up on my back a bit.
But besides the one downside I think it is great and perfect for what I use it for.