Reta is a 90s Czech product, called after its founder, REné TAller. It has some appeal for some people, yeah the top tube on this model is nice. Anyway, it never used nice tubes and overall they were low level. There were quite many producers of rather cheap bikes in the 90s here. Not sure if it was Reta or another brand that went bankrupt after floodings in the early 00s.
I had one some years ago, Reta M1, their first atb model. It was Sachs equipped (as many of them), from about 1991/2, 14kg ish and not really bad. Bought it for about 30 pounds in great condition, and ended up selling it for like 25, which is about what they go for here.