If you've been in any arcades any time in the last while, you've no doubt seen one of these things.
They're very common in (what remains of) arcades, often blasphemously placed where DDR cabinets used to be. At first, it looks like any other cheap, slightly bootleg arcade rhythm game. But grand piano keys is not a rhythm game. It cheats.
The first odd thing is it's a ticket redemption game, which seems weird. How can a rhythm game, which is entirely skill-based, be a ticket game?
You might think it's actually more random, but it actually isn't. It places a hard limit on possible player skill. To work in the ticket-redemption format, the game (supposedly) runs in the "play until you miss a note" style, a la piano tiles (which it is no doubt trying to piggyback on the success of) and other mobile games of that ilk, rather than the arcade rhythm games it finds itself in the place of.
If this was truly the case though, this seems like it could be an endless source of tickets. This is not the case however, as there is also a time limit. The time limit doesn't provide this skill barrier though, that's provided by the scroll speed. This is the way piano keys cheats. By limiting the scroll speed along with having a timer, it places a strict upper limit on how many tiles a player can play in a game.
So, what's the point of this? Well, I find the way these things cheat interesting. Also, just don't give this "game" your money. It's literally just a few seconds of very poor rhythm gaming for £1.