True some customization is not as easy or even at all possible in some things, but I have had curiosity about Alps and some others like Space Invaders but have always been put off by some of those gotchas with layouts and form factors that I just can't deal.
At least there are some nice doubleshots available for Alps, like on some of those old NEXT boards for example, though always the issue of not getting a full set to put on something else due to 'weird' keys.