Thats been MY experience. Not to say that the small joint stuff isn't effective or workable, just that it doesn't work reliably against experienced grapplers.
I've been rolling for some time now. I've rolled with guys who've been experienced in more TMA styles and not so much with BJJ. Many times, these guys (same goes with raw beginners as well) will often panic slightly and start "going with what they know" (read, "foul tactics", hair pulling and everything else -- even though 99 and 9/10s of the time this approach doesn't help them).
Often the first thing they do is try and grab your fingers. I've had this happen so much over the years that I've learned to roll and control position using only my closed fists. Which only means, no small joints to attack. Attacking the wrist of a closed fist doesn't work that well as you might know (with some exceptions; the "top wrist-lock" in catch being one, and that is pretty easily countered).
So experience has just taught me to work for things that are more high percentage against more experienced fighters/grapplers (blues and up). That pretty much leaves out the entire small joint/small circle jits strategy.
Again, much of that can probably work against inexperienced guys / white belts. And perhaps that constitutes most of what one would face in a street fight, etc. But I'm not worried about people who have NO SKILL. I'd be concerned more about folks who can actually fight and present some game.
I'm very skeptical because of the situations in which one might use small joint manipulation:
1. During stand-up when there is no positional control and fists are flying
2. In the clinch when going for SJM is or should be secondary to controlling the body (large joint manipulation)
3. On the ground where you have better control (the ground being an ally) but where against better/more experience grapplers - this will not work and against whom doing so might only invite terrible punishment for even trying.
So I'm left scratching my head about why people place so MUCH emphasis on these things to begin with. But thats just me. To each his own.
For me personally, I enjoy working with folks who attempt such things in training. Its really helped my awareness for such attacks and has shown me how easy they normally are to counter.
I have also worked with guys in the past who try and bite, go for the eyes, pull the hair and attack the groin. They did so because I asked them to (again to develop my awareness of these attacks). And what I discovered over time were again, several things:
1. Against guys who couldn't grapple well (read, didn't work from a functional delivery system), they were as powerless to use these attacks as a baby. Even though they tried, it only ended up getting them in trouble because they had no sense of good posture from which to base their attacks
2. Guys who COULD grapple well, were MUCH more dangerous with biting, eye-gouging, groin attacks and the like - but - still wouldn't often do so because they were more content to play a position based game than an attack-based game. More experienced guys (especially those who are smaller) realize that it's better to keep position than to go for crazy-ass techniques that might only end up putting them right back on the bottom again.
So to make a long story shorter, much of SJM is "ok", but nothing that I'd put a lot of time into. I personally put ZERO time into it because of so many other things that are both easier to execute and are infinitely more "high percentage".
The question becomes, why go the more difficult route when there are easier paths to follow which actually take you to more places, more often, in the end?
But that's just MY opinion. I could be wrong.