I’ve an Osprey Savu 4. Fits my waist perfectly and doesn’t shift around. You have to stop to take it off to access the pouches. Even getting drink bottles back in their allocated slots is a nightmare.
It has its place. But I have a cycling rucksack with a 2l bladder, room to stuff a 1.5-2l bottle of water from the shop in the helmet holding area, and space for a small bottle each side on the waist strap (like a lumbar pack). A couple of frame bags, and a 750ml bottle on the frame. I still have to buy water on my rides because I guzzle so much.
End of the day, it’s water carrying that’s critical to me, and the rucksack beats the lumbar pack for that purpose. I’m in a mountainous, Sub-tropical area with higher than expected UV all year round.