>>2037824 (OP)I mean, if anyone else remembers their driver's ed class, and the little booklet the DMV gives you to study, before you change lanes, you check your rearview and side mirrors, then you shoulder check because there's blind spots, THEN you merge.
you still need to shoulder check. mirrors are convenient because if you see something, you aren't going to merge anyway so you skip the check. but you still have to check before you DO merge.
mirrors on bikes either require a helmet mount or they have to be huge and in the way.
I experimented putting a wide angle mirror down on the fork blade, which was out-of-the-way enough, but the field of view was negligible.
shoulder check wins.