I weigh around 185 lbs (but like most people here would like to loose some weight before race season). I ordered the Rocky Road (for riders between 185 and 225). But Tom accidentally shipped a Mocha boom (145 to 185 lbs). On a trainer it seems a little bouncy. On the road, it seems appropriate. Even so, Tom shipped me an insert to stiffen up the boom from one flavour to another (but I haven't done that yet).
Other people's comments include Slowman's review (
http://www.slowtwitch.com/...bikes/titanflex.html) -- he preferred the stiffest boom. A TF I test rode before buying also had the stiffest boom available and it easily soaked up the road ripple. On the other hand, Ironstevie (on this forum) went from Mocha to Vanilla (softest boom). If you're unsure, ask and Tom will probably ship you a couple of booms allowing you to return the one you don't want.
The ergostem is stable once you crank down the bolts. As john points out, it does have teeth to prevent slipping at the joints. john's also right that it is obscenely heavy (400g versus <200g for a fixed stem). There are index marks at the joints so you can record the position as you adjust it.
I somewhat disagree with john's point about an ergostem meaning the bike doesn't fit. One of the _many_ reasons I went with the TF is because every bike shop (and there are some good reputable ones in my area) I talked to told me they had a bike that would fit me. But confusingly, they all had different bikes leaving me wondering who to trust (some of my early posts/questions on this forum are about this problem). The TF with its boom and ergostem allows me to adjust the cockpit and seattube angle in a way that a fixed frame bike simply cannot do. With that, I felt certain the bike would fit.
On top of that, my flexibility have improved considerably since I started dabbling with yoga 2 weeks after getting the bike. That's allowed me to slighty increase the drop from the seat to the aerobars -- something that is an easy adjustment with the ergostem. I expect/hope my fitness and flexibility will continue to improve permitting/requiring subtle changes to the bike fit.
My TF also has an Ergomo powermeter which is giving me some insight into the effect of positional changes on my power output and speed. Again, the boom and ergostem make this possible.
Sometime in the summer or fall once I'm dialed in, I will get a fixed stem (likely titanium or carbon) as I finish training for IMFL.
Hope the comments help. Feel free to ask if you have more questions.
Rob