That depends on where you play, how many simultaneous effects you need, etc.
If you roll your own PA, or there's a shortage of DI boxes where you play, then the XLR out would be a plus for the B3. Ditto if you play solo bass or do a lot ambient stuff, and want to combine tons of effects. It would also be a good arrangement if you have external pedals that you would like to put in between some of the Zoom patches- kind of like having an effects loop in your B3n...
I have experimented with a B3, still own an MS-60B for now, and just acquired a G5n. For my particular circumstances, I much prefer the new features and control layout over the old.
If it made sense to me to pair two Zoom pedals for bass, it wouldn't be a B3 and a B3n. A B3n + MS-70CDR could be interesting, but two B3n's, or a B3n and a G5n would be more likely. These things are cheap and selling like hotcakes, so it's not hard to find even the latest models at a good price.
That's good advice, thanks... all I needed to hear since I do play around with ambient solo bass at home.
I have 2) Eventide H9 Max Pedals and a Zoom B3n and an ME-50B chained together...
I should'nt have used the word "overkill" as much as redundant.
Hell, I'll just buy the B3 as I hear great things about it....
Thanks for the input