A builder once told me about a DIY version of the mentioned product -
suitable only for tile roofs though....

Cut a width of flywire (get the aluminium type used in flyscreen doors
- very tough and long lasting). The width is cut wide enough to run on
top of the first tile and under the second so it is held pinned into
place. The other edge runs down over the gutter and is folded and
clipped over the outside edge of the gutter (you would need to find
something suitable to clip it). Nothing except fine particles can get
through it as the 'uphill' edge is firmly sitting under the second tile
and leaves, where leaves can't get. I've been meaning to do it myself
on my own roof but haven't got to it yet - so can't be 100% it works,
but I'd be very confident it would.

Cheers
Glenn