Simpler is almost always better
I'd however go for at least an Isolette II with Apotar on Prontor-S, I like the extra performance of the lens (yours looks like an Agnar) and the extra set of speeds (yours looks like a 4-speed Vario).
I have come to pay as less as 2 Euro for an Isolette like yours, mostly for parts (damned tiny screws in the focus ring, how easy they become lost...
). The advance knob however is not interchangeable with later models (they are positioned in opposite sides and turn right the other way...)