Question 1: Is it any good in dub or should I seek out the sub?
Because I’d like to rent/buy this movie but not if the dub is completely terrible. Also, I watched the original in dub, GX in sub, and haven’t seen 5Ds which brings me to:
Question 2: Can I watch this without watching 5Ds?
Because quite frankly (and I really hate to say this) I’m not interested in seeing 5Ds. My sister skipped it to show me Zexal (which I’m still in the middle of, almost done with part 1) and I went back and watched the first two episodes and they were… boring? Maybe I watched it at a weird time or something but it just wasn’t fun to watch and I didn’t latch onto anyone like my instant attachments to Kaiba, Judai, and Astral which drove me to continue their shows.
I might give 5Ds another shot after I finish Zexal but I also just wanna watch Bonds Beyond Time. It looks like some dumb fun, which is why I’m even remotely considering the dub.
1) Having gone through both the dubbed and the subbed version while working on my alternate-music project, as with anything YGO for me, I’d recommend the subs more, though the dub here is at least watchable. The dub, as usual, changes more of the dialogue and makes Paradox a lot sassier than he originally was (”I’ve seen a lot of your friendship speeches, but that was by far your most pathetic” or his cutting into some effect explanations), the usual quirk with their writing for Yusei has him be a bit too sassy with his dueling lines, but on the pro side, their music isn’t used awfully here compared to GX and 5D’s’ dubs proper and they actually let it breathe (and they do what I do with the rescore in using some more GX/DM music) and the interactions between the protag trio are nice to hear dubbed (some changed lines notwithstanding). I’d also lean more towards the subbed version because, to tie into your second question:
2) BBT itself does tie into the plot in later 5D’s, as Paradox turns out to be one of three antagonists working with the Big Bad, though outside of referencing it as a flashback to tie him in, it’s not a huge deal. (And personally speaking, I do love 5D’s (subbed of course, not least of which because of how great the OST is, as usual for YGO) and it can maybe take a bit to hook you in since it starts off with the Yusei/Jack dynamic most, but I’d at least give it ‘til episode 26 before you consider dropping it–it does pick up by the Fortune Cup arc kicking off in episode 13, and 25 and 26 are a great end to it, imo. (Your mileage may vary in post-65 world, but that half does have its good sides, too, and I think it still ends strongly despite some of its flaws.))