When capturing MPEG-2, the B frames help reduce the CPU load and dropped frame risk. I've done everything from I-frame to IPB-frame, and I've never really settled on a "one true way" to do things here. It honestly depends on the system, tape, bitrates, and other aspects of the workflow.
It's a beast, but also a beauty.
Generic USB sticks are often risky, and really reduce the clarity (color, sharpness, IRE, luma, contrast, etc) of the image. Some mess up aspect ratio. Many more have failures such as not properly reporting dropped frames. But sometimes it pays off. It really depends on the exact brand and manufacturer of the unit in question.
Glad to hear your project went well.