Personally, I wouldn't get too hung up on the backpack quick fill requirement. Once you've a tank, pump and reel you'll question why you didn't do it sooner. Just keep the backpack topped up with water for when needed. I've a DIY system that consists of a strapped down 350 lay flat tank and a pump/battery box I made. It houses the battery, pump, controller and now also a charger. Really simple, compact, effective. I fitted a quick fill hose for backpack myself, its true as the level drops it gets harder to fill from it, but for its rare use I just make sure its topped up for any jobs at beginning of day. I nearly went for the Face-lift compact 425 myself in my new van, but I had most of the components already. One thing that was putting me off it though and bugging me about the design was the fact it had no sight guage for water level. Being black means you have no quick visual way of checking water level without taking off the lid. Being a lay flat design this can become a concern later in day as water level drops and you may be parked on a slope. All the systems you and others have mentioned are good. But you've got to weigh up the sum of the parts vs convenience. I think some are quite pricey for what they consist of. An alternative idea for backpack fill if it's really a crucial factor would be dropping a bilge or wale pump in the tank through the lid, seen others do this in the past.