I tried a simple test with a 300mm Vitrex TC "blade" this afternoon.
With end fittings rather like wire crimp terminals it fitted the hacksaw easily, but would need a short slot cutting if used entirely within the material.
It had no problems with an oddment of RHS steel angle 6mm thick, but as it is abrading its way with a kerf of perhaps 4mm, it's not the most efficient method.
It had no problem with a small scrap of aluminium-alloy bar, apart from a bit of clogging.
I tried it on the back end of an HSS lathe tool, with a view to suitability for roughing out a form tool, or cutting a length of tool-steel to make a boring-bar bit. Starting the cut neatly was hard because it skidded all over the place, but eventually I made a groove perhaps 6mm deep before stopping – no point wearing the blade further. An angle-grinder with a cutting-disc would be the better choice, and a lot cheaper.
So these abrasive tools are better than nothing, but not ideal replacements for round tension files for making cut-outs in metal plates.
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Anyone tried the Bestway files yet?