For 4 1/2" & 6" wheels, I've been using CGW stainless quickie wheels as a sheetmetal shop owner friend swore by years ago before he passed. Having my work order from Fastenal lately. Better than any other brand I've used, which is many. Home Depot Diablo is fair if you need in a pinch. Pretty sure all the better wheels are a Zirconia based grit, not cerum oxide. Haven't heard of Walter brand before, may check out sometime.
These days I just use electric grinders. My 20 volt dewalt is great for smaller stuff, mobile of course, is lighter & slower speed, which can burn less & is safer for operator. Use a 15 amp corded dewalt with a 4 1/2 or 6" for most uses. Also have a bosch with a variable speed, which can help burn less, particularly with a larger wheel. I keep smaller wore down wheels for tight spots or some curve cuts.
Also waiting on our purchasing guy to get some more bi-metal multi-tool blades with the angled ends. I've cut round speaker holes in door panels with em and some precise light steel or aluminum cutting, mainly in tight spots. Use the 20v dewalt multi-tool these days, while my $400 plus old Fein unit sits in it's box. First got a Fein multi-tool nearly 20 years ago when they were the only choice, but blade cost made use prohibitive. Even now homestore prices or even HF are steep. Amazon has packs for less than 2 bucks a pop according to our purchaser.
I know a little off subject, but very relative. For most of use, if we ain't cutting stuff almost daily, we ain't happy. Probably mainly put aside small pneumatic cut off tools 30 plus years ago due to lack of decent blades back then & have hundreds of hours of cutting practice with 4 to 9" grinders & have the feel for using them. Probably biggest downside is most optimum cutting position generally involves throwing hot s--t right on your arm. Denim arm sleeve helps that.