Fruit Machine Refill Keys was setup back in 2013 to sell Refill Keys to end users.
You do not have to own your own arcade or own your own machine to own a fruit machine refill key.
Refill keys are completely legal and can be owned by anyone.
Some pars and clubs may not like you using them as they feel you may be "cheating" the machine, but this is not the case. It is impossible to alter the outcome of the machine by using a refill key.
Unless you plan to use the key to fill the machine, it maybe more likely to pay out, but who would do this apart from the machine owner?
The only information that could help you possibly win more money from the machine is knowing the hopper balance inside the machine or to see the last bank paid out, this may mean you play the machine or not. It lets you make a more informed decisions whether to play the machine or not to play it.