NIB are currently guaranteeing ECB+0.5% (4%) on lump sums up to €50,000. Another ECB rise is expected by March at the latest, so at that point NIB will be offerring 4.25%. NR haven't always passed on rises in full, but I'd expect them to at least increase the current 4.15% rate to 4.25%, to compete with NIB and Rabo.
There is a risk ECB rates will start to fall, so the fixed rate bond could give a better overall annual rate than any of the variable rate lump sum accounts, but for that risk you get instant access to your money, and the possibility of a higher return (if further ECB rises kick-in).