Just wanted to update this. A customer asked me a couple questions this past Friday which I wanted to share, and subsequently updated the website description.
1- What would I put in MY truck(s)?
2- Is there a difference between the Seiken and the OEM unit?
Answers below:
1- I have and will put in the Seiken.
2- I have had a few OEM units with TOYOTA Labeling on the box I have sold for $469
New OEM Toyota Land Cruiser Brake Booster with OEM Gasket, 44610-60792 | eBay When I had them, I was able to compare them side by side and the boosters are exactly the same. The only difference is that you would pay $170 more from me or $350 more from your dealer, for the cardboard box that has TOYOTA on it, which is fine if you want to frame it

But that is a lot of coin for a box. And of course you'd need to get the gasket which is included in the Seiken units I sell.
In short and as previously stated, there is no difference between the two other than the box it comes in.