"Buyer beware" is the best advice I feel I can give regarding "El Cheapo" brand diamond hones. I've tried them in the past and found that they wear out after about half a knifes-worth of sharpening.
Getting a little more technical, cheap diamond hones are made with poly-crystaline industrial diamonds. You can imagine these to be like ultra-miniature sugar lumps. The fractures between the individual grains of diamond dust (stuck together into lumps big enough to be of the correct grit size) are a LOT weaker than the diamond, and because of this they tend to shatter and break down very easily, shedding the useful diamond that stands proud of the metal very quickly.
Good quality diamond hones are made with mono-crystaline diamonds. As indicated by the "mono" prefix, these are single, solid pieces of diamond, and as a result of this they are tough. Very tough. With no fractures in the grit of the hone, the diamonds do not wear down at anything like the same rate as the cheap versions.
I've known "el cheapo" hones that failed and became smooth after only a few minutes work. I've got good quality diamond hones that have lasted me many years and are still going strong (and I do a LOT of sharpening!)
The cheapo hones also tend to "try and make up" for their shortfalls by having pretty coarse (poly-cryatline) grit when they are new. In practice, I've found that this leads to them being good at putting some fairly hefty scratches into your blade about 20 seconds before the hone wears out and becomes useless for removing the scratches with.
I speak here from my own experience and am simply stating my own views based on that experience.
