I raced with a Ritchey adjustable stem for about half a season, continuing its use in the offseason until I got a frame that allowed me to replicate the bar position. I don't have the pictures readily available but basically I measured the location of the center of the bars (i.e. where the stem clamps it), Sharpied the primary points of a different frame size (where top tube ends, where head tube ends, etc), and figured out that I could use a flat/-17 12 cm stem on a size smaller frame.

That's a long way of saying that a Ritchey stem is totally usable in every day riding. Yes, it's a bit heavier, yes the weight is in an extremely noticeable area (the bike responds slower when making slow speed moves). I'd say the stem was as stiff or stiffer than the regular Ritchey stems I used - due to the massive angle adjustment bolt and the material for the angle adjustment area the stem is rock solid in that area. It's like the S&S frame coupling - they actually increase the stiffness of a lot of frames because they effectively shorten tube lengths. Same with the Ritchey adjustable stem.

For secureness it has a locking tooth type angle adjusting thing so it limits the fine tuning but it also makes it possible to securely lock the stem in whatever angle you want to check.

Keep in mind that a Ritchey stem adjusts a portion of the length. I used a 12 cm stem but only about 8 cm actually angles (I didn't measure, I'm guessing).

I've used a Look Ergo stem as well and that was more like what I expected - flexible, heavy, not very secure (it'd move on you in violent efforts). The Look is much more adjustable and I would use it for radical TT fits and such. On one rider's TT fit I ended up placing the bar in such a way that it was almost directly over the brake - the Look stem followed the head tube straight down. He ended up winning the top Masters stage race, helped along with winning the TT in that stage race.

Speaking of fit almost anyone can get numb fingers. It's normal to see guys at the end of a crit shaking out their hands because in dicey situations you want to be in the drops and many riders don't train in the drops. They're not used to the position, don't adjust their grip properly, and therefore get numb hands. This happens to me if I'm so focused on race events/tactics that I forget about things like moving my hands around (which is second nature to me now). Before you go too crazy with fit solutions for your numb hands:
1. Do you move your hands around, like every few minutes? Hoods, tops, drops?
2. Do you shift your hand within a given position every minute or two? So if you're in the drops do you adjust your grip slightly so the weight is elsewhere?
3. As asked before do you "grip" your bars or just gently grasp them?

If I rode improperly I can get my hands numb in a few minutes. Riding properly I can go 6-8 hours without any problems. In very intense races on extremely rough roads and with the threat of crashes all over the place (Harlem Crit) depending on my fitness I've done 10-15 minutes without any hand numbness to the whole race without numbness.

What's interesting is that I used the Ritchey adjustable stem when I was coming down from a peak weight of 215+ lbs @5'7" (late 2003). I bought a size M Giant because the smaller frames I had were too short up front - my gut prevented me from leaning over like normal, i.e. like the prior 19 seasons I raced. I went to a size S Giant when I was down to a svelte 190 lbs (heh). I used the adjustable stem to verify that I could get the bars properly positioned.

Then in 2009-2010 I finally ordered a custom frame. I'd never ridden a properly fit bike before and I was a bit nervous ordering a frame that would increase my reach (think of increasing stem length) by 5-6 cm. It'd be like going from a 12 cm stem to a 17 or 18 cm stem. The bars also came down a touch, maybe 1 cm. I used the same parts as my prior bike so the bars, saddle, post, wheels, even tires were the same.

My primary worry was that my hands would go numb quicker due to the extensive increase in reach. I built up my bike while out in SoCal at my then-annual training camp. After a shakedown ride I started cranking out 3-6 hour rides like I normally do out there (at home I rarely ride more than an hour or two at a time). I was pleasantly surprised to find that I had no problems with numb hands etc. I had to get used to the extra reach but otherwise the bike worked so well I ordered a second frame (and they are my primary and backup bikes now).

So why didn't increasing my reach by 5-6 cm and dropping the bars by 1 cm give me numb hands? Because I practiced "good hand position management". Although I spend most of my time training on the drops, especially on longer rides (due to a bad back it's more comfortable to be in the drops or sitting totally upright i.e. no hands), I adjust the pressure points minutely all the time. When doing longer climbs (the whole length of Palomar Mountain takes me 2 hours, give or take) I climb on the hoods or the tops, again minutely or coarsely adjusting grip regularly.

Core work helps too but honestly I haven't do much core work in the last couple years and my hands are no different. I've thrown out my back twice recently but my hands are fine