I've been using this Hydration Pack during my navigation and rally training, and it's become one of those pieces of kit I don't really think about anymore, exactly what you want when you're riding.
I love the fact it is waterproof. The waterproof zip is incredibly effective at keeping everything inside dry. It does need occasional lubrication (which comes supplied) to keep it running smoothly, a small amount of maintenance for peace of mind.
The hydration system is ideal for long and or hot days on the bike. Being able to drink while riding means I stay hydrated without constantly stopping, which is really important as I prepare for my Moroccan Rally where dehydration is a massive potential issue. Refilling the bladder is straightforward - you do need to remove it from the pack first as is standard.
Size-wise, it's spot on. There's plenty of room for the essentials—light tools, snacks, a lightweight jumper or jacket, spare gloves—and there's also a discreet hidden pocket that's ideal for small valuables like cash.
Comfort has been excellent, I've worn it for full days riding and haven't experienced any rubbing or pressure points. It fits comfortably over my body armour and, once adjusted properly, it doesn't move around at all, even when standing up. For reference, I'm a women's EU size 38 and am wearing it on the smallest adjustment setting.
One small improvement I'd love to see would be an additional attachment point for the hydration tube on the opposite shoulder strap. The tube stays securely in place, but would love to have the option to route it on either side would make it even more versatile.
It's clearly been designed by people who ride. It's practical, comfortable, waterproof and has all the storage I need for long trail and adventure rides. It's going to be my companion for the Rally for sure!