i had some time on my hands today to do some tests between the single trim an double trim, first was the amount of pressure needed to get a good finish, the single trim seem to need less pressure, but if the angle is changed the single trim needs less, second test was snail trails in this test the single trim out performed the double trim by a long way, dried on bird crap was next i tried both brushes on this they both seemed to preform the same with a pre soak, i still like the single trim better for me but it seems there is a place for both brushes. also as for there weight well aint nothing wrong there at all.