There are different practices regarding inserting the 18 verses of Baruch Hashem L'Olam between the Sh'ma and the Amida in Ma'ariv. This site points to one reason for not saying them:
The rishonim dispute whether one must juxtapose the mention of the Redemption with the beginning of the Shemoneh Esreh prayer even for Maariv. Tosafos (Berachos 4b) write that one must, and explain that the Hashkiveinu blessing that separates the Redemption from the prayer is not considered an interruption because it is “one long [mention of] redemption.” Tosafos also explain that the longer Baruch Hashem Le-Olam prayer does not constitute a hefsek, though some are careful not to recite the blessing for this reason (see Maaseh Rav no. 67).
If I follow the final ruling and don't say the verses so as to avoid the interruption, but am davening with a minyan that DOES say it, should I answer amein to the blessing before kaddish or does that create the same interruption as if I had said it?
This question provides an answer that in a different case, saying a couple of words is not an interruption but I don't know if the cases are truly analogous.
There is a video online which might answer this but I can't get it to work so I don't know if it addresses my question.