Yes, good starter....
Yes, good starter....
Presuming the camera is in good shape, the GS645S is a very good starter MF. Excellent Lens, very good rangefinder system. Just a bit wider than normal for the format... probably equivalent to 35-38mm in 35mm format.
The shutter assembly on this model was very reliable and accurate.
I hope you have the opportunity to handle the camera. Most people are a bit dismayed at the light heft and plastic look of the camera. I will tell you that the frame is a metal frame clad in plastic with textured rubber coverings. They actually stand up to abuse, but not uncommon to find hairline cracks around the view and rangefinder windows.
300 Euros is considerably more than I would pay, unless there is an opportunity to shoot a couple of rolls and some warranty period. There is an exceptional camera repair person in the US on the East Coast, and I typically buy these rough or parts and send them to Frank as he is very reasonable. Fuji still does some service on these as well. However, I am talking about buying $100 US parts cameras in this instance.
Right now there are two on US eBay that close in two days and are currently about $150 to $175. I suspect they will close nearer to $300, but would watch them to see. There was one on Ebay UK that sold around $200US and seemed to be a good condition camera.
Bottom line for me.... the GS645S technically and optically is a great camera. Great starter for MF. Good lens, good rangefinder, very good over/under style meter. Concerns would be condition for a camera that is likely 25 years old. Not highly sought after and not a lot of value (price) as a result. This alone makes these a great starter, but probably not at $300 Euro's ($450 US)
The GS645W with the 45mm lens generally sells in that price range in excellent condition, but remember, it is NOT a rangefinder. It is zone focus due to the increased DOF offered as a result of the wider lens.
Quirk.... Always keep the film under tension until the back of the camera is closed. This is true of all 120mm film cameras that load like 35mm cameras. Otherwise film will bunch up on the takeup spool and you may not get through the roll. I add this because it's too easy to throw the roll in like a 35mm, feed the takeup spool, slam the back closed and start winding the crank. With 120, it's imperative to keep the film tight across the frame opening as you close the back door.
120 film that is loaded into separate film backs, or on inserts, is not as noticably critical, because it's a different way of loading and even newby's tend to keep the film tensioned.