What's the best tool for servicing Shimano external bottom brackets (Hollowtech II) and installing centerlock disc rotors that use the same spline pattern? Looking at either Shimano's tools (TL-FC32 and TL-FC16) or the Park tool that combines those (BBT-9). Similar cost either way. The Park tool goes all the way around which might be more secure but also means you can't tighten a BB without removing the crank. Any opinions or suggestions on similar tools I should consider instead?

I use a BBT-9. The only ones I wouldn't recommend are those that attach to an adjustable wrench or socket, as they tend to "walk" off the splines.

side note: there are multiple sizes (3 I think) of Shimano HTII BBs, each requiring their own tool.

IIRC some BB that are different come with an plastic insert that fits into the park tool. this was the case for ones (english and italian) I used with 105 5800 crankset on 2 different bikes

I once got an XT BB and it was smaller than the installed Deore BB. It didn't come with the tool adapter insert, so another thing to buy.

I prefer the socket style, haven't found walking off to be an issue like it is for cartridge BBs. I like that I can use a ratchet to facilitate getting it screwed in quick and easy, and the leverage I get with the ratchet without having a narrow piece of metal cutting into my hand trying to get a tight BB loose.

Haven’t bought one but intended to get a socket style because I read here somewhere the sheet metal style interferes with the drive side yoke on hard tails like mine

You can reposition the flat wrench style when it hits the frame, not really a huge problem. The flat steel style wrench does however tend to dig into the cups pretty bad. Just cosmetic damage, but get a socket style tool if that would bother you.

I like to use an aluminum socket tool on external cups to keep the damage to a minimum. Bonus points for a 1/2" drive so I can use the big breaker bar when they get stuck.

If you are looking to have the well stocked tool box, why not go with the tools listed in the Shimano DM's for your models of BB. If you don't like the Shimano tool itself, then just find the generic knock off of the same tool.

But if you aren't going to be changing BB's often, I'd just let the LBS or a friend own the tool and use theirs.

i just bought a flat 44mm BB tool made by BW which includes a crank arm cap preload tool. It is solid and worked fine and at $15 cost less than the inexpensive BB, which made some kind of sense to me. It only slightly dug into the cup splines. More torque = more damage I assume

Thanks for this. I have two bikes with BBR60s, and didn't realize that the splines are a slightly different size than the the centerlock rotor lockring on a Fulcrum wheelset. I was hoping I could get one tool for both cases.

Given the above, and that in years of working on bikes I've never removed a bottom bracket (never had one fail), you're probably right. Only time I've needed that tool was to install a bottom bracket on a bike I built up myself. Getting my LBS to remove and reinstall a bottom bracket would cost about as much as the tool to do it, but I'm sure a friend has the right tool, or I can visit the local bike co-op and use the tools there. My office used to have a nice set of tools (bought by our bicycle commuter club) but we moved into a new building the day before our local stay-at-home order went into effect last March, and unfortunately the tools disappeared somewhere in the chaos of rushed relocation.

Rated “best” by Barnett Bicycle Institute. Two handles evenly distributes torque

Cyclus Snap-in handle, Hollowtech insert, and centering rod.

Detail of Hollowtech insert.

Removable insert for 3/8” square drive.
. Centering rod prevents cam out. 3/8” square insert for using a torque wrench.

Stein CBBH. But no centering rod. BBI used to rate it best until Cyclus invented their system.

JA Stein Cartridge Bottom Bracket handle with a SuperB TB-1005 cartridge (which has a 1/2” square drive).

Closeup of SuperB TB-1005

I was going to say Abbey tools and a Snap-On Digital Torque Wrench but that Cyclus thing looks pretty neat. I might have to take a closer look at that unfortunately their website is terrible or at least for me it was couldn't click on any links.

Can just get a slide handle breaker bar for the socket, never needed it but it can duplicate the cyclus tool.