Oldjerry, one of the main criteria is that this should be suitable for people with no DIY skills.
I know it's a bit late but here's my thoughts.
I can see a small problem in that whilist fitting what you describe could be done with little or no DIY skills there comes the need for skills to connect your fitment to tanks , or toilets or whatever plus the dangers or working at heights and drilling holes through gutters and walls.Personally I'd go for something along the lines of an actual fitment that is fitted into the guttering as a convential downpipe fitting is.
Also one other problem is the size of the hole and hose. Being quite small there is a higher likelyhood of it blocking up so filters and more regular maintenance is probably required.
Just my thoughts.