Hola, Daniel; mi placer poder ayudarle.
I'll post what I heard about it. I never had one of this, but I'll add one "turbo" add-on as soon as I have time to build one.
What I know is that:
- in some cases, it is incompatible with some clock-dependant devices; some 82104A card readers were mentioned as not working correctly with some speedy 41's
- it enhances power consumption, reducing battery life.
Other then these "features", it is harmless for the calculator itself.
About availability, I was also told that it was fairly available in Deutschland (your 41 came from there, right?) as a kit, not exactly as a "commercialy availble" merchandise. I saw some different "versions", one of them with a magnetic switch mounted inside the calculator, aligned with the middle frame. This way, a small magnet could be used to toggle from "speedy" to normal. Others, as mentioned, used dip switch or key combinations/sequencies.
That's all I know from other contributors at the MoHPC.
Hope these informations are acurate (if I did not change them) and helpfull.