It meets the minimum safety requirement of 1/2 water and 1/2 vinegar brine. Of course more vinegar would give them a longer shelf life. And I'd take care with "Pack prepared cucumbers into jars as tightly as you can" as it is easy to over-pack the jars and cause a poor distribution of the brine.

As to the type of vinegar - that is a personal taste thing. Cider gives a more mellow taste and slightly sweet while white is sharp and has more of a bite to it. Both are safe as long as they are 5% for sure but most so-called kosher (garlic flavored) recipes do call for cider rather than white IME.

Dave