But if the line angle is too low, the massager my not be heavy enough to come back down (travelling into the wind).
The Lifting Messenger, solves a lot of problems with the steep line, as if properly working, it will actually climb a vertical line. A steep line will also solve the problems of non return though some sort of brake may be needed at the bottom to cushion the stop.
Fill with lollies, each stapled to a simple parachute, and suspend the box upside down from a kite line.
When ready, pull a cord to release the velcro to let the lid swing open dropping the lollies into the wind. Be sure the down wind area is clear as a hundred kids all running after these lollies can case a lot of havoc!.
A Kite which flies too low will have a strong pull, but little lift. A kite that flies too high like a genki, or delta, you will get very little tension on the kite line, even though it is mostly upward. A good choice for this is flowforms, rokakkus, and cody box kites. Deltas if loaded with a drogue and other tails can also work well. The extra drag from a drogue helps to stabilise the kite and stop it flying at too high a angle. This way it catches more wind, and thus pulls harder.
A flowform is a good lifting kite, is sparless and commonly available, in small to very large sizes. The sparless nature of the kite means transport is easy, just stuff it into a bag and throw that in the car. The large ones may require some heavy anchors to keep them from flying away. It is a good kite to buy, though with care an good sewing skills can be build yourself.
Rokakku's are also a good choice for lifting kites, are spared, but flies very stable in a wide wind range. You can build them yourself but the large kite shops sell them too. They are often thought however more as a artists kite due to the large flat surface area.
The third is a Cody War kite or 'Man lifter'. These also fly stable but are harder to transport and longer to put together. The design of this kite was specifically for lifting people at the turn of the century. They are also harder to come by if buying, and not so easy to build.
The one I used a lot for lifting is a 1.5 meter genki (half size) with a turbo tail (drogue), I call Ol'Faithful. It is old, stretched, and made from the wrong material. It is a wonder it became such a good, long lived, wide wind range kite it is. This kite (with the drogue) flies in strong winds without problems and doesn't fly too high either.
A normal genki flies so high and well that the lines own weight is prone to make the kite wander! It also doesn't flutter or collapse, when the wind dies, but glides forward like a huge airplane wing. If used for a parafauna drop it is likely the kite will wander all over, be pulled forward. All the while the messenger only moves down wind keeping a meter or so above the ground.
With a really good high drag tail, to lower the kites flying angle, and keep it from wandering, a genki can be made a good lifting kite, but as the 'normal' genki size is 3 meters wide, it can remain prone to sudden sideways movement due to a unequal gust of wind.
Everything I said able for genki's apply equally well to delta kites. They does fly quite as high as a genki, and are more stable in turbulent winds. They also don't glide, but rather just fall when the wind dies. Other than that a drogue makes them fairly good lifters, in the same way as a genki.