- Should I put the pronoun between but and also as what we can see in Cambridge's example?
It's fine for also to come at the beginning of a sentence (or in your case, of a declarative clause that's coordinated to another with and), but in that case it's a sentence adverb, and should be set off with a comma (or, in speech, with intonation):
[…] but also, it outperforms the previous devices.
Personally, I find that just a tiny bit stilted in your sentence, but it's not unidiomatic (let alone ungrammatical). Rather, I think your sentence just flows a bit better if you move also to modify only the predicate, as you suggest based on the Cambridge Dictionary example:
[…] but it also outperforms the previous devices.
More generally, Google Ngram Viewer shows that but it also is much more common than but also it.
Note, though, that this is only possible when it actually makes sense for also to modify just the predicate, e.g. because the subject in the second clause refers to the same person/thing/entity/whatever as the subject in the first clause. So in the following sentence, for example, you can't move the also after weather:
Not only were the people very friendly and welcoming, but also, the weather was clear and warm and dry. So everything about the trip was just perfect.
This is because there's actually nothing special about the also in "not only […] but also"; you can also use "not only […] but" with "too", "as well", "so", "even", and various other words and expressions whose meanings are the same as, or subsume, that of "also". (In fact, it's not unheard of to use "not only […] but" without any such expression at all; but I wouldn't recommend that.)
(By the way, I should mention that although in these examples, the position of also determines whether it's modifying the whole sentence or just the predicate, the position of also does not always determine exactly what it modifies. For example, in a sentence like "She also works there", also could be modifying either "works there" or "she". So, don't overgeneralize from the above examples.)
- Is my sentence grammatically and idiomatically acceptable?
Yes, except for the above. I'd also recommend adding a that after I believe, to make your sentence a bit more readable; "I believe not only" is a fairly intricate way to start a sentence. Google Ngram Viewer finds that "I believe not only" is as common as "I believe that not only", but if you look at the actual uses of "I believe not only" on Google Books, you'll find that very few of them mean the same as "I believe that not only […]". So in sentences like yours, "I believe that not only" is presumably much more common.