I have the B&D one sunnybob. 1st, IMO, "powerfile" is a silly name for it, because as a file I tried it briefly, and frankly, while it does remove metal, you could do better (and more accurately) with a blunt tooth brush! (OK, slight exaggeration, but not by too much)!
BUT I bought it for a specific job, namely sanding down the (concave in 2 directions) insides of the front wings of an MG TC 2 seater kids "sports" pedal car (mix of laminated ply glued with hard-drying waterproof powder glue and epoxy filler). They're over 1 metre long and about 60 mm wide at their widest point and included steel mounting brackets internally.
For that work it's done a reasonable job and was the only power tool I could find (at a sensible price) that would do the job - the insides of those front wings were so tough that I soon gave up with hand sanding. Yup lazy, (+ bad back)!
Mine is the one that comes in a plastic case with a choice of 3 "arms" (I got it from Axi in UK, the only ones I could find here were the bare, single arm models). Those 3 arms allow you to fit sander belts of 2 different widths (if remember correctly half and quarter inch) and of 2 different lengths. Sanding belts of from 60 to 180 grit of the 2 different lengths are freely available here (B&D own, & aftermarket) and aren't too expensive.
The tool did the above job fine (after I'd done some practising - especially the 60 grits can be very abrasive, especially if you push too hard, and/or get the angle wrong!!!) and with the 180 belts I ended up with a finish that was good enough to paint to a standard good enough for a child's outdoor toy. Used carefully the belts last a reasonable length of time too - about the same as any other thin& narrow sanding belt.
I don't know anything about the sort of work you're proposing but GUESS it would work OK.
Apart from the job I described above I haven't found another use for the tool yet, and frankly, I doubt that I ever will. It's certainly virtually useless for "proper" filing of any job with any degree of flatness and/or dimensional accuracy. Apart from anything else, the belt is not stable enough.
So for me anyway, it's a specialised "one-off usage" tool, though I would add that I do believe that all these "DIY power file"-type tools are actually based on a professional car body workers tool (usually pneumatic I believe).
However for my own job as described above, I doubt that I could have purchased any other tool at a sensible low price that would have done that particular job for me.
HTH