Mystery Price for MB 144?

[theodore94]

I found this MB 144 on FB Marketplace. I asked the seller (not a collector/dealer) about it, and we got to talking. Turns out it ended up selling for $300+, which is way more than I would have expected! I'm wondering if there's anything particularly special or collectible about this pen that would justify the price. The pen has already sold, so I'm not exactly asking for advice... but I can't help but wonder: did I miss something important? Something I should look for in the future? Or was it just an overzealous buyer?

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There's also a video here: https://drive.google.com/drive/folde...Wy?usp=sharing

It's "lightly used". Based upon that and the pictures, it's been inked.

Let me know! Thanks so much!