My current razors are open combs, Gillette New Type and iKon. The only blade that I could call bad performers in these are Gillette 7 O'Clock Yellows. They just gave rougher shaves in the open combs which is a real shame because they were my favorite blade to use in my Merkur 38c
Merkur Futur with Astra Greens.
Had burns for nearly a week and lost more blood then when I had a cut in my leg 6 inches long and 2 deep... bought 200 blades, threw 199 in the trash and framed the friggin blade that wanted to kill me...
The worst, and the cheapest blades available in Sweden, must be the Swedish Rijk.
Too thin and flimsy, peel the skin of your face but leave the beard intact
Unfortunately I have to add Kai to the list. Jagged edge, incorrectly sharpened and expensive too. Highly overrated and overpriced. Regret getting 50 of these. My skin does too. Terrible.
Haven't found anything unusable so far but Derby Extra is the worst, really struggles to cut through my hair. No intention to ever buy any of the walmart/no name/obscure third world country blades mentioned here.
So far, for me, it's Merkur. I only used one so far, from my 23C, and it was awful. I have another one that came with my Progress, still debating on if I'll use it or not. Might give it a whorl just to see if it was technique or the blade. That having been said, I had no issues with the Astra SPs I used next.
Dorco 301. By far the worst of the twelve brands I am sampling. Blood, blood & more blood. And neck irritation that looks like a case of hives. Dumped two after the first shave.