Understanding 〜てなんだけど


> 「あんなのを欲しがるなんて、連邦も物好きよねえ。長いこと使っておい **てなんだけど** 、 **たいがい得体は知れない** のに」
>
> 「まあ、戦場なら役に立つんじゃない？
> こっちも阻電攪乱型はいるみたいだし。〈ジャガーノート〉の方は、あんな歩く棺桶なんか調べてどうするんだよって感じだけど」

86─エイティシックス─Ep.2 ─ラン・スルー・ザ・バトルフロント─〈上〉 安里アサト

They are talking about a communication tool.

How should I understand the usage of the bold part? Namely, the construction
〜てなんだけど? By the way, does the たいがい得体は知れない mean "I don’t know much about how it
works", literally?




This kind of なんだけど can be understood as a contraction of
"A(しておい)て(いう/するのも)なんだけど", roughly meaning "it is
awkward/inconsistent/contradictory etc. to say/do after A"

Hopefully the examples explain:

  * 食べきっておいていうのもなんだけど、おいしくはない。 It is awkward to say after finishing it, but it was not really delicious.
  * 来てもらってなんだけど、あんまり手伝ってもらうことはない I appreciate that you have come, but a bit awkward to say, there is not much to do here.
  * 自分で言うのもなんだけど、これは完璧だ It is not right to say this about what I did myself, but this is perfect. (In this case, there is no A of the pattern)

I don't think the translations exactly convey the nuances of the Japanese
sentences, but basically なんだけど indicates the situation/action of the speaker
is not very consistent with what she says/does.

たいがい means basically "overall" or "most of the time". たいがいX is usually with a
word X of negative connotation. For example, たいがいいい加減だ means someone is いい加減
most of the time, if not always. So in this sense たいがい makes the description
softer.

So the bold part means _**it may be silly to say this** after having used it
for such a long time, **but the tool is rather fishy**_.

* * *

Note that なんだけど itself appears more "normally".

  * 明日のことなんだけど Regarding tomorrow('s schedule)
  * 子供が病気なんだけど My kid is ill, so...

