Bought this as a replacement for my first one. Reason, I lost the closure for the bladder. That said, I've used my first one for 3 years, the bag that is used to carry this on my PFD is great as well. On my boat, when my skirt is on my cockpit, it's very hard to reach things under it, like a water bottle. This pak works well and the whole setup sits above my skirt and seat back. The tube can connect to the front of my PFD and is easy to access while paddling. I've not experienced the setup ever leaking either. While it does add to the weight of my PFD when full, I haven't found this to be a problem, even after having to do a water exit on my boat.
The Hydrapak® Elite 1.5 liter reservoir can fit in the sleeve in the back of the Poseidon or in the outside pocket of the Tactic Pack accessory. The reservoir can be turned inside out to clean and dry. The hose detaches for easy cleaning and drying.