The compatibility of Olympus OM lenses is generally true, but with the odd exception of the power focus lenses, which lack a focusing ring for manual focusing. (For that matter, it is also not really true that all old Nikon lenses can all be used properly on all their new camera bodies.)
We also had a longer conversation about OM lenses and he really knows his stuff. So if you have any issues with an Olympus OM lens I can only recommend to give him a call or sent him a mail.
Compared to many other manufacturers, Olympus took a slightly different approach to lens grading. Where many companies released consumer-class kit lenses made out of inferior products or designs, all Olympus OM lenses were made to the same high standard. The differentiation of the lenses was done simply by their maximum aperture. Referral to the below list of released system lenses will show the 'consumer' model of the OM 50mm for example has a maximum aperture of f/1.8. There was a 'prosumer' model released with a f/1.4 maximum, and even further a professional model with a maximum aperture of f/1.2.
Olympus OM lenses are excellent value for money. The Olympus OM 35 2.8 is remarkably small and compact for a wide-angle lens. It weights only 177 grams (the first version at least) and is absolutely no burden to carry around. In fact, the Olympus OM 35 2.8 is a great travel companion and backup wide angle lens. This also makes it a great option if you are using a smaller cropped sensor camera. While it is tiny, the lens still feels very solid and is able to take a knock. The lens is very well made and does not feel cheap or plasticky. You do get a lot of quality and advantages for a very reasonable price.