I had some cuttings root successfully recently but they died. On close inspection I discovered that they had been effectively strangled due the clamping force exerted by the collars. Cuttings that hadn't rooted experienced similar crushing of the stem. This is an appalling design flaw. The collars need to be made of a softer material that would be more forgiving, especially for when the stem of the rooted cutting thickens. I've noticed some being sold in the US on Amazon as "Premium Grade Foam" that is described as non-porous, but none appear to be available elsewhere, including here in the UK. However, the collars I have are not neoprene, but a foam, so are likely to be the same product anyway, yet still not good enough. The only other option would be to bore out the centres a little to reduce the pressure. This matter sorely needs to be addressed by the manufacturers, whether it be Ez-Clone, X-Stream, or whoever.