Thanks Morten.
The camera arrived this morning, it is actually an OM-1n. In very good, clean condition with everything looking and sounding normal. It still has its original hotshoe.
It does not have a 'split image' focussing screen, instead it has just a central microprism circle. I'm pleased about this because when using longer lenses part of the old split image used to 'black out' on my OM-10. I also think it makes manual focussing quicker.
I like the exposure controls being around the lens (aperture, speed), this seems so much more intuitive than having some on the lens and some on the top plate.
The film advance is smooth, and the shutter is so quiet compared to the Om-10!
I think I'm going to enjoy this camera!