Nemo will probably pop in an ID this for you sometime. In the meantime, I found a long discussion in the FPN archives that suggests that it might be made by Reform.
I don't know anything about these, I've never held one or seen one in person. I have noticed it being similar to some Geha pens I have from the '50s and early '60s, looks like an ERO too, also shaped a lot like Reform and Senator pens since there was a lot of copying going on then by smaller German manufacturers. I saw the eBay listing and the seller said it's from an area around southern Germany and Switzerland.
If it has a working piston filling system and a gold nib you ought to be OK for that price. Here are some great pics in a sales post from a Spanish FPN member.
I recently found out about some Lindauer pens from the Bodensee area (southern Germany, Switzerland, Liechtenstein) that look very much like this pen. I'm currently researching these in what little spare time I have these days. Interesting pens to say the least.
Congrats on the pen, let us know when you try it!