I like a hydration pack for hiking in hot weather – I drink more if it is easy. But, itis hard to clean.
For real backpacking, I would stay away. There is always a chance of a leak. If you don’t screw things in quite right, all of your clothes would be wet. That risk exists for a day hike as well, but for a day hike, I’m probably only taking polarfleece and raingear so I’m not as worried if they get wet.