As a holiday concert experience, however, the show, ably performed by the SpeakEasy cast, amuses and induces toe-tapping. For those grumpy about sentimental Xmas entertainment, “Striking 12” delivers cheer, uplift, and plenty of musical talent while remaining blissfully devoid of the usual saccharine, holiday-show sentimentality. Striking 12. Book and Lyrics by Brendan Milburn, Rachel Sheinkin,…