I've not used them, however I've used the same other set that Racketman has used over on Photography on the Net in your thread on that forum asking the same question. I bought his earlier designs which push onto the flash head with a little clip - I see that he's refined the design with a much more secure wrap-around.
That said pretty much any of the small softbox attachments is going to give similar-ish performance in terms of diffusion since they all basically do the same thing, increase the size of the light source relative to the subject. Kaiser bounce shoes or other attachments to raise the heads up (or the flexi-arm attachment) are all options for letting you place them where you want as the ringflash mount on its own isn't big enough to give room to fit softbox attachments to the flash heads.
Larger magnifications will always be a trial because you're moving the whole setup much closer which cuts down on working distance.
The smallest attachment I've used is an oblong concave dome and works on the principle of changing distances instead of softening light by a larger area. The concave design means that light sourced from the middle is further away than light from the edges - in theory on a 3D insect (or similar) subject this means a reduction in the light hitting at different distances on the subject and thus softening the differences in the light. That said I've not seen anyone making them (these ones were the caps off a stain remover product). StevB found the idea years ago though I've not seen much of him around the net these days. The bonus is that they are much smaller than softboxes but they still need a spacer (Kaiser shoe works great) to raise the head up.
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