I've ordered a Malling Jet blackcurrant, an older variety that is also said to be the latest cropping. According to the Chris Bowers website it has been superseded by newer varieties which I take to mean more even ripening like Ben Tirran. (no problem for me as blackcurrants ripening over time avoids a glut)
I obviously won't be able to comment on this variety until this time next year. It will be planted over winter and I would expect a small evaluation crop next year. Yes I know you are supposed to cut them down after planting so the plant establishes but I'm impatient sometimes and blackcurrants are pretty tough.
Spreading the harvest time using a combination of varieties is well worth it. I have a very early kind that ripens as early as mid to late june and another that ripens mid july. So if Malling jet takes the picking season into august that is great.
Blackcurrants are so useful, extremely tasty and easy to grow.