Was out for a few beers with friends in Peel this afternoon/evening, random £500 jackpot machines are basically a fixture in every single pub here, almost always at least one, often two, and sometimes three or even four.
They are capped at either 250x or 500x stake for the jackpot, depending on the 'generation' they belong to, and RTPs run from 88% to 94%, with 90-92% being around the average.
I won't get overly involved with them, but I will lob £20-£60 at them, and I go in on £1 plays, for a little bit of a death or glory attempt. On many of them, prize is linked directly to stake, with stakes running from 10p to £2, so on 10p play your jackpot is £25, whereas on £2 play it's £500. Going in on £2 play can be pretty ruinous and lead to a very unsatisfactory experience, I've settled on £1 per play over the years, which means a jackpot of £250 and a few more spins for your money.
On this occasion I've managed to land four of the bomb scatters, they are the best of the three bonus rounds to land. Unlike your normal online slots they have to land left to right on every reel, so whilst they don't need to be on winlines, they do need to be on 1-2-3, or 1-2-3-4 to count (for three or four scatters respectively), and of course 1-2-3-4-5 is five scatters. (There are bonus rounds with turtles and starfish as well that work the same way, but the bombs have the best pays.)
Here I've got them on 1-2-3-4, you then have to pick a bomb from the top touchscreen out of three options, I asked a mate to reveal the bomb for me and he picked the best one of £120, the other values revealed as £70 and £100.
Paid for the session and the meal and the bus fares with money left over, was only £40 in when this landed.