A very interesting link - thanks koalar. Despite the checking tools you can buy I, some time ago, decided that I would always replace a DMF if doing a clutch which featured one. Undoubtedly you might get away with the old one but I feel that the failure rate is high enough to be not worth taking the chance.
Of course ECP are in the business of upselling if reasonably possible, but it was nice to see it stated in writing.
I'm quite attracted to the idea of these solid flywheel conversion kits and have spoken to garage workshops who have fitted them. I've always felt quite nervous about the stories of gearbox damage and rough vibrations I've read, but the mechanics I spoke too said this had not been a problem they had had to subsequently deal with and they'd not had one back after fitting. I recently became aware that one of the big manufacturers supplies a "special" driven plate with longer travel springs - so there is more movement available between the hub and driven segments - so maybe there is something in this? I would actively seek out one of these I think if I were considering the change. However I think it's a wee bit of a risky think to do so, personally, on my own vehicle, I'd replace a DMF with a DMF. One of the factors I considered when looking for a new car was that it shouldn't have a DMF!
Here's a quite interesting link about the subject in general:
https://www.eeuroparts.com/blog/single-mass-vs-dual-mass-flywheel-why-convert/