Just a quick heads-up that Aristocrat MK5 games are playable in MAME (and have been since at least 0.180), with some issues. As of 0.253, over 200 sets are supported, including several setchips.
* Games run at double speed.
* Bill acceptor is not supported yet.
* Serial comms systems/interfaces (e.g. ASP, QCOM, SAS, Mikohn etc.) are not supported yet, however Hyperlink features such as Cash Express can still be triggered and will attempt to pay the appropriate jackpot (obviously without any jackpot credits being won due to no link connection) and then give a "call attendant" error - jackpot lockups are cleared by pressing V.
* The USA platform may give a coin diverter error when inserting coins, which needs to be cleared by opening and closing the main door in order to continue playing (occasionally, a New Zealand game may also do this, on these machines, use the jackpot key (V) to clear the error or just reset the machine with F3) - note that coin lockout isn't emulated yet so the games will continue to accept credits even in lockup/audit mode.
* Sound is not working properly (or at all) in some games.
* Flashing symbols and graphical animations of wilds/scatters sometimes fails to work due to unfinished emulation of the video chip (this includes the Penguin Pays feature where the penguin is moving all over the place), although in all cases the wins are still paid.
* Older style games on the USA platform (coincidentally, all of the ones where the sound isn't working properly) can lock up if a hard/hand pay occurs, with the only option being to switch to a clear chip (setchip) to reset the memory and start again - a workaround is to switch to 1 coin per credit, as it only hangs if the payout is not a multiple of coins.
* Some NSW and all Venezuelan and Peruvian games (the latter which use the standard/NSW platform, not USA) hang after a certain number of paid spins (or poker hands in the case of Multidraw Free Games) and need to be reset with F3 in order to keep playing.
* Venezuelan/Peruvian games show a bill acceptor error on startup, which has to be cleared by pressing V - a workaround is to change the bill acceptor protocol to VFM4.
* A number of games are bad/corrupted dumps and do not boot at all, the chips need to be reacquired from somewhere and redumped.
* Button labels below the game screen are guesswork due to lack of photographic evidence and might not be correct for each game - the labels can be changed in the Video Options menu if the game itself supports multiple button layouts, for example 45, 90 or 180 credits; you can also set the games to "Screen only" to hide the onscreen buttons entirely.
* Reversed button labels on the USA platform (e.g. with "Play x Lines" on the bottom row similar to the Australian machines) are not currently supported, also due to lack of photographic evidence (additionally, only the "gamble enabled" layouts are supported, so for games where the double up option has been turned off the artwork will still show Gamble and Take Win buttons).
* Button names in MAME's "Input (this Machine)" menu are currently hard coded thus only one label variation is shown here, however this does not affect the ability to press the buttons themselves e.g. if MAME is showing bet multipliers of 1, 2, 3, 5, 10 in the input menu but the game is set to 1, 2, 5, 10, 25 instead, the rightmost bet button will still bet 25 credits (or it will play max lines if the button panel option is set to reversed).
For those who are new to setting up slots, especially when it comes to using the right setchip settings on the USA platform, some setup instructions can be found in the MAME source code, which is also mirrored on GitHub for those who don't want to download the entire MAME source.
https://github.com/mamedev/mame/blob/master/src/mame/acorn/aristmk5.cpp Feel free to post your big emulated wins or any issues you have with the games.
Updated April 16 2023: The source code is now in the "acorn" folder instead of "drivers". It's under Acorn because the MK5 shares its ARM250 architecture with the Acorn Archimedes A3020 computer.