I cannot shave with a Derby Extra. I have tried them in a number of different razors. I have revisited them a few times over the years. I finally gave up and passed them on other shavers.
So far for me it would have to be the Dorco ST 300 Platinum which is made in Korea. Horrible from the start, pulling and tugging and a very patchy shave.
I was using the Gillette blue (SH) blade on the Gillette plastic handle entry level shaver(8 RMB at walmart or about $1 USD), dull and simply hopeless. Not until a couple weeks later I swapped out the Gillette blue blade for an Astra SP, what a night and day difference just by blade change alone.
The 1961 Gillette Super Blue I pulled fresh out of a pack was really, really dull and tuggy, worse than anything else I'd ever used. From now on, nothing older than a Spoiler.
Oh thank heavens. I thought I was the only one that didnt have good luck with an Astra in a Fatboy. I was not terribly overwhelmed with it in a slim adjustable either.