PBs are around 1.15% return average.
Better than many savings accounts and much better than a poke in the eye with a blunt stick.....
And the prizes are tax free, which is advantage if you are a prosperous plumber.
Prizes are random, but the more bonds you have, the more regular the prizes get, and the nearer your return gets to the notional average.
If you have less than the max (currently £50k) you can have your winnings automatically reinvested.