Just tried the banh mi at the relatively new Bon Me food truck today while at SOWA. Had the regular roast pork banh mi and it was pretty good. My favorite banh mi in town is still the one at Pho Viet at Super 88 in Allston, but this one was also pretty good if a little pricier ($6).
The Bon Me version sandwich is standard size with a crackly and light baguette, and had a nice carrot/daikon slaw, a nice mayo sauce, and good overall balance. Despite it not being spicy enough for my personal tastes, nor the roast pork being as savory as the one at Pho Viet, it was still pretty good and I didn't mind paying an extra $2.50 for the convenience of having banh mi available in a food truck close by. They were plenty busy and service is efficient. They take credit cards with those cool iPhone attachments.