Hah I did a SRAM EX1 when they first came out and I would NEVER do one again. You can just do too well with much lower cost parts now.
I have done a number of Box Two XW-based setups.
Bear in mind the Box cassettes are just Sunrace cassettes with different labeling. I first heard this on a BikeRadar review, IIRC. I have bought both and compared them and the only difference is the lock ring label. Also I have done Box Two and Box Three cassettes, on Box Two both the ebike version that starts with 12T and the regular one that starts with 11.
There is absolutely NOTHING wrong with Box Prime 9. The Box 2 derailleur is really nice, and has the pivoting cable mount which is nice. Also if I were you I'd spring for the Box 1 single shifter as it uses a slickerier cable and housing, but more importantly has a handlebar clamp that makes your life much easier on initial install and down the road since you don't have to cut the grips off to get it off the bars.
There is no need to buy the Box chain. I use the SRAM EX1 chain which I am sure you are familiar with. It is 10s compatible but works perfectly with Box drivetrain and is cheap at around $25.
BUT... over time I have left Box behind. It was sort of a premium workmanship product but I found too much that works better for less money. First of all, Microshift makes a 9s Advent cassette whose cogs are
all hardened steel. And it costs like $40. You lose a couple teeth of capacity at the top end but thats a small price to pay. Also the Microshift is something the Box is not: Pinned completely together so drivetrain force is distributed across the entire cassette body. The Box 3 cassette also has its bigger cogs bolted to the next cog down. Thats why you have to use that spacer at the cassette on the inside edge. The Microshift has no spiders at all and all cogs are full-sized. Heavier but max-durable which is better for a BBSHD power level.
I also found the Microshift Advent derailleurs are less expensive and work just as well. And being a cyclist who is pedaling, and always looking for just the right cadence, I decided to try the Advent X version which is 10s, less expensive than Box, and still has the hardened steel rear cluster. I have visited all manner of brutality on it and no question I would do another Advent X if I had a build to do.
This bike has a Box 2 XW derailleur, Advent 9s steel cluster and SRAM EX1 chain.
Do they connect to the motor and have the shut off for while shifting so the chain doesn’t snap?
No. Nothing from anyone does that. You have to install a gear sensor inline with the shifter cable to get that function. OR you adjust your technique. I personally have only had one bike with a gear sensor on it and have never missed it, because I have adapted my shift technique so I don't have a problem. This applies to any mid drive motor even though the article is focused on the Bafang motors:
This is a common question on BBSHD and BBS02 motors, so I thought I would write up a quick post and describe what can be done, and what I do.
talesontwowheels.com
Lots of details on parts/drivetrain options for Box etc. here:
Mid drives up the ante on the required competence of the builder. Read this so your bike lasts without things breaking or wearing out early.
talesontwowheels.com
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