The Hayyei Adam Hil. Tzitzit 11:9 opines to not make a brachah nor to rely upon a small Tallit - except as an all day reminder - and to davka wear and make a barchah on a full size Tallit. "...Y'rei Shamayim Lo Yismoch al zeh [Tallit Katan] k'lal.."
Mashma, he does not favor the common Eastern Ashkenazic Minhag of Bachurim not wearing a Tallit Gadol. This seems to support the Western Ashkenaz and Eidot Mizrach Minhag of Tallit Gadol for all B'nei Mitzvah