Well, welcome aboard. My first instinct is to ask for more information, as you will be able to get more accurate advice. That said, the general opinion on Olympias (if I may be so bold) is that they are well-made, reliable machines--some of the best produced. And in today's typewriter market, $15 with shipping, is a very good price, especially if the machine is working. 

I cannot open the link you posted, so I can't see the typewriter. But since you said it's green, I am guessing it's one of the earlier carriage-shift SM series of Olympias, like the SM3. These are excellent machines, and that is a terrific price. (Just make sure the seller packs it securely! This is absolutely critical.) The only caution I would mention about the machine is that the carriage-shift Olympias may not be as pleasant for lengthy typing sessions as the segment-shift machines. This is because the carriage shift seems to require, for me anyway, somewhat more effort than the segment shift models. You may not even notice the difference, or simply get used to it. But I wanted to mention this.

Fleetwing wrote:

I cannot open the link you posted, so I can't see the typewriter. But since you said it's green, I am guessing it's one of the earlier carriage-shift SM series of Olympias, like the SM3. These are excellent machines, and that is a terrific price. (Just make sure the seller packs it securely! This is absolutely critical.) The only caution I would mention about the machine is that the carriage-shift Olympias may not be as pleasant for lengthy typing sessions as the segment-shift machines. This is because the carriage shift seems to require, for me anyway, somewhat more effort than the segment shift models. You may not even notice the difference, or simply get used to it. But I wanted to mention this.

It's actually a traveller de luxe from the 70's, not an SM series. The address only works if you copy and past it.

OP: I assume that you're in Denmark (or you want to type in Danish) given that the keyboard and character set this machine has?

​Otherwise, I wouldn't hesitate to buy the machine. $15 is a no risk investment, and the Olympia Traveller is a solid, well-engineered typewriter. The action is on the heavier side, which is not a bad thing if you're a good typist, and there's a touch control to adjust it slightly.

The noise level for this model is average compared to other ultra-portables, but there are many factors that ultimately determine how noisy a typewriter is, some of which you can address if you need to make it a more quiet machine.

The machine weighs around 4.5 kg, (5 kg with its carrying case/cover). I've travelled several times (by air) with this exact model, albeit using a different travel case, and found it to be a good typewriter in this role; that shouldn't come as a surprise given that's really what ultra-portables were designed for. However, if I was going to buy just one typewriter and was planning to use it a lot, and there wasn't any need to actually travel with it, I would not buy an ultra-portable but a standard model instead.

Yes, it's a fine machine for the price - grab it.  You will probably want to 'upgrade' at some point, say to an SM3, 4, or 9, but this is a bargain that will get you going and will be useful as a spare and back up if you do ever get another.  Good luck.