We've had the spanish nylon wasters for a couple of weeks now, and I must say I like them.
I also know that some other arma sweden members use them (since I ordered some for them).
They work great and safe in drilling and above all sparring. We can go pretty much full speed using lacrosse gloves, helmets, throat protection and joint protection, and even though they can sting like hell serious injuries seems unlikely. The long grip is really an advantage here, the control you get allows you to get a nice balance between speed and power in cuts.
I've got some nice bruises from thrusts to my ribs, and an overzealous thrust to the throat might be dangerous, but probably safer than a shinai. I have one of them Hanwei rapier vests that I use when I can be bothered to, and those removes the potential dangers from thrusts with the nylons well.
Im recommending new students to purchase one of these in our group now, the price will be around the same as a shinai + wood waster (especially since Im no fan of shinais, even weighted ones).
One reservation I have is that the waster slide almost too well in the bind, sometimes proper bind maneovers can be difficult. that is compared to steel though, they are still better than wood and shinai in most aspects.
another reservation is that the steel crossbar (on the spanish model)can be dangerous in halfswording and wrestling moves, some tape out on the ends should do it.
here's a video clip of me and a sparring partner testing the nylon wasters:
http://www.youtube.com/watch?v=TBnDRpixHnA
