Any Xlab product with gorilla cage and a bottle with a curved groove should work fine. I’ve never launched with that set up.

That’s more aero than without?

What is a curved bottle?

I distinctly remember TT stages where pro riders did have bottles. There was a TdeF ITT where Froome didn't even have an aero bottle as he had a large water bottle much like we would use on training rides. Made me wonder. Seems like they're concerned about hydration than aero,

Is there any truth that if your going to have a water bottle in the triangle, that it's better to have two?

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Indoor Triathlete - I thought I was right, until I realized I was wrong.

Look at your bottle. See a grove 2/3 of the way to the top? If yes, should be fine. If not, more launchable.

Likely sponsor obligations. Tacx or elite only ever get their names on camera via quick shots on the trainer or from the bottles.

Ditto the XLab recommendation with a Gorilla cage. I have a Cobb JOF 55 seat, so I have the Cobb BTS bracket made to connect directly to my seat. But, I have a pair of basic, but strong, Profile cages.

You have to remember that only about 10-15 riders in a TdF ITT actually care about their time. The remainder are most like just mailing it in and treating the ITT as a recovery day making sure they beat the time cut-off so they can keep riding the next day. Hell, some even do a wheelie on their TT bike across the finish line. In other words, for the majority of the field, staying hydrated during the ITT is way more important than their time.

Froome having a round bottle during an ITT is different. He's always in the hunt for the GC, so his finish time is important. However, the Pinerello TT bike that he rides has a distinctive flare and cut-out on the down tube right at the bottle bosses. I'm guessing its aerodynmics were designed to accommodate a round bottle.