depends on what Felt setup...
Round bar bullhorn with clips, maybe some gains to be had.

Devox/Bayonet (or whatever they call it now) probably not much.

I think Tririg has an aerobar shootout on the Alpha's page.

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My Blog - http://leegoocrap.blogspot.com

I have the rounded bar with clip ons.

I went from the Bayonet 3 on my IA16 to a Tririg Alpha X. I would do it again in a minute. Tririg does compare the Alpha X directly to the Bayonet 3, so they claim a material difference. I will go with that. I did a regular 10 mile time trial test run before and after, and it was faster according to my power meter. Not hugely scientific, because it was N of 1. But, I am OK with that. Here are all the improvements I like:

1. Much more aero-- you can see it in the thinner, wider profile of the base bar.
2. Base bar has rough grip area by the brake levers-- I eliminated the rubber hoods and do not use grip tape. This is probably a tiny bit more aero.
3. Massively superior extension and arm rest attachments-- they are both more aero and more secure
4. Better BTA mount-- I was using an XLab Torpedo, which is pretty good. The Alpha X is way better
5. Better cable routing-- the Bayonet 3 is pretty clean cable routing, but the Alpha X is better
6. Massively lighter-- I think the Alpha X is like a pound or more lighter than the Bayonet 3 setup
7. Better stem-- IMHO, the stem clamp on the IAxx stem is poorly designed and prone to failure; Alpha X eliminates this threat

Where do you stash the di2 junction? Still in the front or in the stem now?

I am not Di2 yet; that is next on my upgrade list. I do not know if I will put the junction box in the Alpha X compartment or the IA16 compartment on the front of the head tube. I will probably put mine in the Alpha X, but I am not sure what is easiest for charging access.

The other thing I want to investigate is whether I can use this in one of my extensions and then permanently hide the junction box. But, I would only do it if I can figure out a clean way to route the Di2 wire if not through the end of the extension.