Beware! Rant mode- ON!
I'm going to go out on a limb here and say for the record that internal headsets are stupid!
Yep! I think this is one of the single most unnecessary "developements" in recent bicycle technology. (They've been done before on steel road bikes from the 30's) I have yet to read one reason why they are better than a conventional threadless headset with pressed in bearing cups. Other than "looking cool", I can't for the life of me see what reason anyone would want one.
As if headsets needed another standard to deal with. And then, there are several internal types, making it even more difficult to service and find replacement parts for. Let's see now, I have a bad headset and I need a new one. My bike shop has several nice ones in the case, but hey! Mine's an internal headset! Guess I'll have to order the one and only choice that'll fit my bike. Or better yet, I'll have to find a bearing supply store that has the correct cartridge bearings on hand, and hope they aren't more expensive than a Cane Creek S-3 headset that can be had for around $50.00 from most any bike shop.
Internal headset = less choices, and more hassle to service.
Then you have the whole machined head tube thing, which really baffles me. Why on earth would you place the bearings directly on the frame tubing, risking future damage to the area, and ruining a complete frame. (Which I have already seen several examples of, by the way.) Sure, maybe you have an internal headset mountain bike and have absolutely no problems with it, but why have that risk? It's not necessary, and the internal headset doesn't work any better than a conventional one. It's not like conventional headset frames are failing from their headsets, unless they get really loose, far beyond the point it would take an internal headset to deform a head tubes machined seat for the bearings. And once that bearing seat is deformed, than it's bye-bye frame set!
Internal headset = risk of frame failure and doesn't perform any better.
You could argue that the bearing seat area is reinforced to prevent deformation. Fine. But I could do without the extra frame weight, thank you! You could argue that the increased diameter usually associated with internal headsets gives a more stable downtube/top tube/headtube junction for welders to work with. I say, it's not necessary, and even if it was necessary to have this more perfect union of tubes, then you could do it without using an internal headset. Sounds like a justification for the existence of the internal headset, and not a happy by product of it. You could argue that there are internal headsets with pressed in bearing cups. I say "Wha...? Why not use a conventional pressed cup headset and save all the trouble?"
Internal headsets = Justifications that make no sense.
Finally, for a 29"er, I think internal headsets are even worse. With the inherently shorter headtubes, the leverage forces being greater due to the longer fork legs, and the fact that these are mountain bikes, I think the chances that you will ruin a frame set due to a deformed bearing seat are even higher. Why? A conventional pressed in head set cup headset alleiviates this potential problem.
Internal headsets= bad for 29"ers!
Sure, you can ruin a frame with a regular headset installed. Yes, that can happen. However; the rate for conventional headset/frame failures to internal headset/frame failures in my experience points to a larger number of internal headset frame failures by a large margin, and the internal headset hasn't been around yet a quarter of the time that I have been working on bikes. It just doesn't need to be that way.
Again, other than looking cool, why have an internal headset?
I tell you, they are just plain stupid!