Google Translate was rough on that one, but i think i get what the dev meant:
If you sub, you may see additional (different) pixel art animations (My guess: probably not being included in the game) and "sneak-peak" at pictures (probably game over CGs etc.) that will be included in the game anyway at some point.
Development stays the focus though and monthly benefits may or may not be included.
The ROMS/ Demos can all be buyed with the back issue, so no need to subscribe to the plan just for them.
The 500, 1000 and 2000 yen plan have the same benefits.
I you want to give him money but expect a return, i recommend going through his articles to see, how often he actually includes additional content.
Keep in mind: Even if you subscribe, you won`t see past releases. You need to buy a "back issue" for those months.
Her more information`s for that:
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