" Is it worth growing both summer and autumn rasps if you don't use them for jam etc and only for eating fresh?"
We reckon that the later ones - 'Joan J' in our case, are a good bet, GG.
When I moved some new plants (from suckers) up from 'The Patch', they started right away, but we also had a few mid-summer ones, and plonked them in as well, to fill any gaps.
They're doing a few berries, but the JJ are now beginning to heave around a bit, so we may be OK for a crop this year!