I don't own a Merkur Progress, but everyone says it's an aggressive adjustable, so not exactly recommended as beginner's razor or for somebody that has sensitive skin. Don't toss it.
Those are RK brand blades that are made in India, I heard they are not bad, but I never tried them. Feather DE blades are extremely sharp, they induce fear in some inexperienced people. I never had a problem using them myself, but I was very experienced before I ever used one.
You should be fine with them in a Henson I would think since it is a mild razor.
How old are those ASTRA blades? They haven't been made in the Czech Republic in very a long time. Astra as well as most other DE blade brands that Gillette owns are made in St. Petersburg, Russia at the Petersburg Products Int. factory, although a few brands are made in India.
After the collapse of the Soviet Union, Gillette (this was before P&G bought Gillette) went on a buying spree, buying up popular trademark brands and factories in Europe. After the new St. Petersburg factory was opened in 2000, they closed the old factories including Astra Diu in the Czech Republic where Astra and Nacet brand blades were made, and consolidated production in St. Petersburg.
RayR wrote: