Saw your flap wheels and ordered some myself, coincidentally the exact same brand. Been using the 3M sliver cutoff wheels, happy with them so far. Yes, huge difference in quality and longevity between the cheap stuff and the good stuff.
ragtop ... just got one of those a few months ago, definitely something that needs to be in the arsenal.
Some of those seemingly useless flanges were probably a necessity of the stamping process. The parts need a "flange" around the perimeter for the stamping press to grab so the metal can be stretched into the desire shape by the press. It's usually an additional process to put it in another machine that trims off the flange, which when possible they might exclude to save money. Then they probably fill those cavities to prevent buzzing, rattling or "tin-can" sounds. People like to hear a "thunk" more than a "tink"
