It is the Czech Model 1920 helmet, which is a modified Austrian helmet with the comb added. These were used briefly after the war and were the first of numerous Czech-designed steel helmets. It is actually an extremely rare helmet and the price probably isn't bad.
Why the comb was added is a mystery to be honest. I've read that the Czechs tried to simply make it look different from the Austrian helmets, and more like the French helmets.
Following that pattern the Czechs had another half a dozen helmet designs. While France and the UK stuck with what they had, the Czechs came up with all sorts of patterns.