Provis jackets are truly spectacular for spotting from a long way away in the dark, but can be unpleasant to ride behind in a group.
(I remain sceptical that being visible from a long way away gives a real safety benefit in terms of not being hit by motorists, but it's awesome bling, a completely retroreflective jacket could give you WTF factor[1], and I suppose it might help rescuers find you quickly if something goes wrong.)
[1] The process by which recumbents get given more overtaking room and better junction priority respect than regular DF bikes.