How many times are you likely to use the 28mm f2 at its widest aperture?....Will it be enough to offset the inconvenience of having to cart around seperate size filters?.....As has already been mentioned the 2.8 version is far cheaper.....When I used Olympus I had 28mm 2.8, 50mm 1.8, 100mm 2.8. A compact outfit with all the same size filters.

Are you aware that the mercury batteries that power the OM1's meter are no longer available in most countries?....There are alternative silver oxides available of slightly higher voltage, which can be used with a Wein Cell. since I don't use Olympus anymore I cannot vouch for their accuracy.