Flap disks are okay in my opinion but are rather expensive.
Best bang for buck are sanding disks for the grinder.
Use a 3M backer, most costly part, around $20
Then ask your supplier if they carry ARC abrasives. IWS in Slidell LA does carry them and they are inexpensive, around $1 each. Make sure you ask for the coated disk. This is not your typical coating, this coating makes the disk white, looks almost like they dipped it in wax.
Coating is a coolant and lubricant that, as you sand/grind, melts and keeps the disc from loading up. I have use 3500 of these over the last 4 months and am seeing 3x the life compared to flapper discs and regular sanding discs.
Don't worry the coating does not turn to a liquid nor does it leave residue.
If all else fails PM me and I can get you more info if interested. I am not a salesman for these so this is not an add.
I was looking for a better disc and to me these things are the cats meow.