all neo geos ( i think) take a cartridge. Some are one slot, two slot, 4 slot etc. Im going to guess that the machine in question is a one slot conversion or custom build.
A one slot will still work just fine. Bieng it has a multi cart in it you probhably wont swap it out for other titles, but its nice to know you can if you get bored with it... A 2 or 4 slot gives you the oppertunity to switch games on the fly, a one slot you can still switch games but you have to do it manually. THink big huge cartridge that goes in from the top super nintendo style.
That looks like a dynamo "cut corner" cabinet. "cut corner" refers to the control panel notches. Pretty popular cabinet. Some companies used that as thier dedicated cabinet but that was also a popular cabinet for ops to buy new (empty) and build your own game. Such as a neo geo or whatever other popular conversion or kit games the op decided was popular at that time.
Does it have a 19 or 25" monitor? For $300, if it works well and its a 25 inch, id say thats a good deal. If its a 19, meh. However i do need to keep in mind that you are in hawaii. Its not like it is here in the 48 where we can make a road trip to another state to get games. Taking your limited market into consideration, if you want it, grab it.